2015 High Miler

For the tune that’s on the truck now, it was no different. Crispier but not really harder. Tune was already pretty good on the shifts. He warned me that it would be considerably firmer but it’s good in my opinion.

McCoys in Garland. $4200 out the door and replaced the rear main that was leaking as well. I never noticed it but was told by a couple of techs that it was leaking. Took 4 days. Very satisfied at this point.

Trans feels good so far. The list of issues echos many of the things I’ve read here. Mostly seem heat related. New setup has not got to 115 yet that I have seen. Drove it back from the shop over 130 miles, and it never hit 100 but it was 40 out. Builder said it’s built to handle 700 HP. More if it had a hardened input shaft. Hoping I never have to have it out again….

I hope to get it back tomorrow or Saturday. It will have quite a few updates and hopefully the last trans repair for quite sometime.

I changed it twice in the 100,000 miles since it was swapped. I used AMSOIL on both. On Monday when I noticed the issue, I checked the fluid. While not bright red like new, it was not burnt smelling like the last one was.

I did not flip the pill as I was not aware of this until about a year ago and it already had 80,000 miles on the new one. This one will have a bypass if its not done once I get it back.

I was fortunate. It was a goodwill gesture from the dealer to get it covered.

I found a shop in Garland that is going to fix and update all of the weak points. Price point was very fair. Imo. im hoping it’s as good as the price. With the extended mileage on this truck, I’d get nothing for trade in so I’ll fix it and keep driving or make as an extra vehicle. It’s still in great shape as it’s always been a highway vehicle. Waco to DFW, Houston, Austin and San Antonio. I‘ll share where once I get It back. thanks for the help

I'm on my second GM transmission. The first one died at 122,000 and the second has died at 225,000. Very little trailering, its been though the gears a few times but it has not been beat on IMO. While driving to DFW today, about 70 miles from home, it started to shudder and jump gears with no warning. I made it to work and then drove about 10 miles to where I am staying and it was very iffy if I would make it. Not sure what to do at this point. Does anyone know of a good rebuilder/replacement if DFW/Central Texas area? I'd like to fix it one last time and be done. Should have done that last time but GM paid for half of it then. Need a trans and converter and install. This one has had a tune on it to help with the converter issues but I guess I was too late to save it.

The resonators helped a little. But not $250 worth of help. It still has a drone at the same RPM's. Its a little softer than before and most people compliment the sound from outside. I probably should have bought a tuned system but at the time, I was not expecting this much of an issue with it. Maybe I'm getting old like the truck LOL.

I had the exhaust system smoke tested and no leaks were found. Back to square one. I dont know how else the exhaust can get in to the AC system other than the air intake.

yeah, it was initially taken in for the trans replacement, then it was getting exhaust gasses in the cabin after that and they said that the exhaust manifold "donut" had come loose. They fixed that and then about 20,000 miles later, it started again and that's when they said it was a cracked manifold, bad gasket etc. $3500 fix. From there, I put on the headers, y pipe and exhaust. Still smells in the cabin when stopping. IDK WHY I have not thought to smoke test it... will do that asap. Thanks!

Thanks for the bump, but I guess you missed the part about it doing it prior to those changes and that is why I made the changes... It started after I had the trans replaced at the dealership. The dealer said it was exhaust gaskets and a cracked manifold. Neither was bad when I removed them. The dealer doesn't know what it is or "how it could happen" but I think they just dont know and are throwing guesses out. So I am trying to diagnose it myself.

This. Great tire in almost any terrain, quiet, lots of mileage, and with 4x4, you will not have any issues w traction. Been through 2 sets and about to order my third set of 305/50/20.

I’ve been having this issue for some time. Probably 80-100,000 miles. (I feel like it started after the dealer did a transmission replacement but can’t get anywhere with them.) The short of it is when I stop at a light, I’m getting exhaust smell in the cabin through the AC. Doesn’t do it at all going down the highway but as soon as you get off and stop at a light or whatever, the smell starts. When I took It to the dealer, they said it was an exhaust gasket leaking and cracked manifold and needed to be replaced at $3400. F that BS. I now have long tubes, stainless ORY pipe through an X to dual mufflers and tail pipes out the back. I started with the headers and Y pipe and progressed on back. None of this helped the smell. I like this truck a lot and don’t really want to go buy an overpriced truck right now. I’d like to figure this out. I'm fairly knowledgeable about mechanical stuff but I cannot fin where this is coming from or how to fix it. It really only does it after driving, then stopping at a light or stop sign. I’ve posted about this before and did not get a lot of response but the site has grown and I am hoping someone has some ideas on what to check. thanks in advance

X piping is immediately after the crossover near the trans crossmember. It’s a prefab stainless kit. I’m surprised the x is loader than an H. Maybe I misunderstood. I heard a straight X and duals and it didn’t seem this loud, but I didnt ride in it. My truck isn’t that loud outside, even at 3/4-full throttle. So, I would need 2 Vibrants for my truck. Any particular length or size? thanks for the reply.

I’m looking for info on resonators and their effects on exhaust sound. I need to quiet the drone at low rpm. It’s a little ridiculous. Lol You may have seen my thread regarding my exhaust system on my truck. LT headers, 3” ORY to xpipe, dual 3” 12559 magnaflow, 3 to 3.5” 12” long tips. I’m either installing resonators or different mufflers. 85 mph is fine at 2000 but 70 at 15-1700 is annoying as F! Ive read several pages on the exhaust thread but honestly I didn’t find what I need. Looking for some insight. .

Update: I added an x pipe from the headers to 2 magnaflow 12559 mufflers and dual 3” tailpipes in hopes to calm it down. It did for the most part but it’s actually louder in cabin now with drone from 1500 to 2000,which is about 70-78 mph. I needed the tailpipes as it was getting some exhaust smell in the cabin at idle and I was getting an exhaust stain on the corner of my bed, presumably that is the exit point while driving. I can promise that it was not louder inside than out. It was really loud with the single magnaflow and turn down. It used to sound like you were matting it even if you weren’t, especially when it down shifted. Made my wife anxious lol. Now it’s actually just where I’d like it, except for the drone. I would like to know how it sounded with just that added tail pipes but w from what I have seen previously, the x pipe should have helped as well so I did It all at once.

Sorry to hiljack but I am Interested in this swap as well. I have a 2015 5.3 w 225,****** and climbing. I see 2017 and 18 L86’s for sale with trans and transfer case for about $5-7000 quite often. Can I swap the 8 speed or should I keep the 6 speed? I have a few shops locally that can do the swap for me. thanks for the feedback.

PN for max tow radiator? My 2015 recently cracked on the drivers side near the outlet.

I have a 2015 5.3 w headers and ory to a single in and out Magnaflow 12259, then a short tail pipe just over the axel housing and a short tip. (Basically cut the resonator off and put a small 8” tip on due to way too raspy without it.) 90% of the time, is fine. But on occasion, it’s just a little on loud in the cab. Right around 2200-2500 while in the gas, it gets a too loud. I was looking at adding a tail pipe but I like the look of not having one. So, I’m looking at options. Different muffler? Different size tip? I’ve read quite a bit in the exhaust thread but nothing I’ve seen quite like this setup. I did Not read 203 pages, though. It sounds really good wide open but half throttle, eh… Would a larger tip help or make it worse? It’s just the 2.75 ID now. Was thinking about 3” from muffler back to same area or just do a 3” full tail pipe and try to hide it up higher under the bed more. it’s something in the tune for certain peddle positions that it’s worse than others. Kind of like when I remote start it the put the key in and turn it “on” it makes a different tone. Anyway, just seeing if anyone had any input or ideas. I could put the resonator back on but it was just too quiet…

Apparently, GM figured out the cooler stat worked and added it to your new truck, just as they did to other year trucks. I’m sure the heavier loads expected with a 2500 kept them from doing it previously. Wish I had known about this trans trick prior to replacing my trans at 119,000 miles for $5000. Now I’m at 218,000 and hope it’s not too late to flip it or add the bypass pill. My truck trans runs at 195 at 55 or 95 mph.

I’m trying to understand something that keeps being said. I’ve seen it posted more than once on this thread that no ‘stat can cause over heating due to not keeping the fluid in the cooler long enough. How would a ‘stat help an engine that is too hot? Once it hits the opening temp, it can’t slow down the water by closing because the heat already hs it wide open.

Thank you, Marty. I def agree with your perspective but wanted to make sure it would not effect the vehicle negatively. Thanks again!

I’m in need of a new Tstat and have been looking to see if there is a benefit. Most say no but the last two posts appear to say otherwise. I have An HPTuner and credits. I live in central Texas and am not too worried about the heat but I am considering the 174 v the 160. Current mods are headers and ORY to single straight through muffler and a mild tune. The 174 seems a like a good option. As far as heat builds horsepower in drag racing, I’ve never heard that unless it was on methanol. @pokismoki @grumpybear would like to know more. Thanks