MrRotorsports

This may seem a little off topic at first but I am looking to see what others have done regarding exhaust systems for a 3/5 or 4/6 drop on the 2015 Sierra? I initially installed a 3/5 drop with a Borla touring rear exit system. I don't recall having any exhaust interference then but now that I dropped it to the current 4/6 when I hit a dip in the road the rear axle pumpkin would strike the exhaust pipes that were above it. After two or three times of this happening I went under the truck and found the brake hose bracket was bent down. As a temporary measure I cut the pipes off as they exit the muffler and removed them. This sounded great at idle but when you were driving steady-speed and it went into 4-cylinder mode it sounded awful - resonating in the truck and buffeting like it does when the rear windows are down at highway speeds. So I bought a 33" long Magnaflow baffled muffler and two down turn pipes and had that installed. The exhaust exits down and out to the passengers side exiting right in front of the axle. Once again, it sounds great idling and under strong throttle but I can't stand it at cruise speeds. It resonates under the bed and is sooooo annoying on a long drive. So, before I throw any more money at "trying" the next combination I am hoping some of you can tell me what system you have used that fits with my now 4/6 stance? I also have a Hellwig sway bar set in the truck so that tightens things a bit between the axle and spare tire. Ideally I would like exits behind the rear tires but at this point I just need something that exits back far enough to eliminate the buffeting. I have not been able to find a really good exhaust shop in my area (Mid-state South Carolina) who I trust to do a set of custom pipes. If anyone knows of one I would be willing to travel a few hours in any direction to get this done.

I've been working on my 2015 Sierra SLT and thought I would post a few pics of it so far. I started with a Borla rear exit touring system and Belltech 3/5 drop, added KMC 22 inch wheels with 305-40-22 Grabber UHPs, a BackFlip G2 Tonneau, a Bedslide 1000 SE, 30% tint all the way around and Putco fogs and backup bulbs. I took off the factory oval tube running boards and temporarily installed a used set of ABS boards off a Yukon. I don't love the look of them but needed something to stop my 9 year old from wearing the paint off my door sills. I have purchased a set of the AMP Power Steps but now I am thinking they may extend down too far. Does anyone have the AMP Power Steps on a 2014 or 2015? If so, how far down do they extend from the body? Would you mind posting a close up picture of them extended? I have already purchased a bunch of stuff for the next stage, I just need to get the time to install them. I have Hellwig front and rear sway bars, an AirLift 59209 Slam Air kit with a Wireless One compressor kit, A K&N cold air intake, Murimoto Sierra Spec headlight kit, Rigid Hi/Lo driving lights and Rigid diffused flush mount backup light kit. When I install the sway bars the Borla pipes will be right in the path of the rear bar. I love the sound of the Borla touring muffler so I plan to cut off the back half and have a local shop custom bend some new pipes that exit behind the rear wheel, pointing out and down, but tucked up tight to the rockers. A pair of the GMC 23238760 tips should finish it off nicely. Next stage will be a programmer but I have not decided which one yet. If anyone has a programmer they are really happy with please let me know which model. I hoping to find one that will firm up the shift points. The transmission seems to have a light slip between the first few shifts. The dealers says they all do it but I still prefer a firmer shift. I can't help but think a firmer shift would mean a better life-span for the transmission too.

Hi Newm. My vibration only occurred between 73 - 82 mph. It didn't matter how I drove it or what the road surface or road conditions were. It was very noticable in the steering wheel and seat bottom. If you had a drink in the cup holder you could see the rapid vibration in the bottle, to the point it "rattled" and annoyed you. It feels like a whole new truck now - just like it should have when I bought it new a few weeks ago. Go figure...

I am pleased to report that my vibration is fixed, at least for now. Last Wednesday morning I dropped off the truck for it's second evaluation. My dealership had purchased a "Pico" meter (not sure of the correct spelling) that helps them locate the source of a vibration. They pinpointed the driveshaft as the main source so they replaced it. Apparently it was a lot better but they still were not fully satisfied so they also ended up replacing two tires while they had it there. I returned last night from a 1700 mile trip (SC to Miami and back) and it was an absolute pleasure driving this truck. Of course I was expecting it to start vibrating again halfway there but it did not. There was not a hint of vibration at any speed and I even managed to knock down 19.1 mpg with the cruise set at 80 mph all the way there and back. Hopefully it does not reappear in the future but for now at least, I love this truck again. Now I finally feel confident enough to start accessorising it. I have the Bakflip F1 and BedSlide coming tomorrow, and the 3/5 drop, Borla Touring and 22s are next. For those of you dealing with this I would ask your dealer about this Pico meter. Again, not sure I have the spelling or name correct but it was a device that GM Engineering reccomended the dealer use for analyzing. They said they had another truck that was vibration in the 35 - 40 range and the meter pinpointed driveshaft vibration on that one as well. I guess they now have two happy customers, and I'm glad to be one of them. I sooooo did not want to have to drive a Ford or Dodge!

Holy smokes! I am soooo sorry for writing a novel. It looked so much less wordy in the writing window. Please accept my appology.

It is amazing to me that Silver Spaceship first posted about this issue in August of 2013, yet GM still has not fixed the issue – and actually carried it into a second model year! It's also unfortunate that I just traded by smooth riding 2011 SLT in for a $48k 2015 SLT vibrator. It has the same issue as many others in this thread, and I have already wasted a bit of time at the dealership trying to figure out the problem. I wish I had read this thread prior to my trade instead of stumbling on it while I was looking for a solution. I had them bring my truck in from another dealership’s stock so never drove it before taking delivery and I had no clue what I was getting into. I have to say that my dealer (in Florence SC) is the absolute best. They are truly trying hard to get it solved. The General Manager even insisted on personally coming to my office (45 minutes away from his dealership) and dropping off his own demo, taking my truck back to the dealership, and then making the swap again as soon as they had mine fixed. He said they would strip parts off any vehicle on the lot and swap them into mine if that’s what it took. To me that is an incredible statement that they are 100% focused on their customer service. For that reason alone I will stick with them to get this thing figured out. I actually love the truck, except at 73 - 82 MPH. Mine seems to always have a slight vibration in that range but sometimes it manifests itself as an outright shake. Sometimes it settles back down to a light vibration, but there is always at least a light vibration present in that range. They have done the road force thing and even installed one new tire, as well as rotated them into different axle positions. It did not seem to change anything. The service manager explained that they had at least two other vehicles they have been working on with the same complaint. They tried tires, driveshaft and even a replacement rear axle in one of them to no avail. They wanted to keep mine and do some exploratory surgery but I suggested I keep driving it and they call me when they have found a fix on one of the other's in their possession. For the record, it is a 2015 SLT crew cab, 5.3, short bed, 2WD, 3:42 gears, 20 inch wheels and the Goodyear LS2s. I had the same size LS2s on my 2011 with no issues. After the 2015s first trip to the dealership did not fix it the General Manager and I took out another 2WD SLT from the lot. It was an identically equipped truck and had almost the same vibration at almost the same speeds. Clearly there is a design or equipment issue repeating itself. After all that history, the real reason I am writing is to see if anyone has experienced this vibration issue with a 2015 crew cab short box, but with the 6.2 liter option? I read the first 163 pages of this thread, as well as the last 12 (got lazy in the middle) and I did not see a single posting about a 6.2. They all seemed to be with the 5.3, 6 speed and a mix of 2 and 4 wheel drive. Of course the 6.2 has a different engine, 8 speed transmission, different driveshaft and a heavier duty axle so the driveline is completely different. I drove a 6.2 off mu dealer’s lot for 4 days (over the same exact path I drive this one to my office every day) and never noticed even a hint of vibration in it. I actually loved every inch of that truck – from the incredible power to the drivability of the 8 speed – but it did not have navigation or cooled seats which were options I really wanted. It had the same wheels and tires as mine, it was 2WD with the same suspension package, but it rode smooth as butter. It would be great to know if anyone in the forum has a 6.2 that vibrates. I know I am getting long winded now but my last question is about modifying my truck. A very good friend of mine is the GM at American Luxury Coach (they are the ones that build all those awesome lift trucks you see at the Chevy/GMC dealerships across the country) and I was planning to have them install a 3/5 drop with aftermarket 22s and 305-40-22s. When I found this vibration I asked if he had seen any issues before. They process around 400 trucks a month, lifting them 4 or 6 inches and then shipping them to GM dealers all over the country. They are certified by GM and the trucks are covered by the full factory warranty so certainly he would have heard if there were issues with the vehicles he was delivering. He honestly had no idea what I was talking about. They have lifted thousands of 2014s and thousands of 2015s and he was not aware of any issues relating to vibration. You would think the first thing someone would do was look at the up-fitter and blame their suspension modifications. So, that brings me to the theory that maybe their lifting the trucks is actually improving things and eliminating the vibration in the trucks they ship? Maybe that slight change of driveshaft angle is helping? I suppose it could be the removal of the stock wheel and tires (replaced with mud-tread 35s or 37s) but I have read a few posts where rear leveling kits actually improved the vibration. So, after all that background, should I proceed with installing the 3/5 drop and 22s and see what happens? Since it will be performed by a certified GM up-fitter and I can prove the vibration was there from the get-go no one can’t say the problem is due to the suspension change. I could do it in stages, adding the drop first, drive it for a week and see if it improves, and then add the wheels and tires. That would let me know if one or the other changed things. Or, should I just push to swap the thing out for the 6.2 I drove before I get too much money invested into this one? I already added tint, an electric tailgate lock and some LED bulbs upgrades but I could cut my losses before they get too much bigger. Has anyone else seen an improvement after lowering their truck?