I appreciate the feedback! Yea, just make Lew aware of your mods and he will adjust the tune to take full advantage of them. I should also add that I just did the paint stick gas pedal mod (link) yesterday. Wow, holy crap, that forum post is not wrong. Made the tune feel much better and more responsive. I had to use 2 paint sticks, though (broke one in half, shoved it up underneath the plastic).
Truck details Make/Model: GMC Sierra Year: 2014 Engine: 5.3L L83 Trim: Work truck (blue blood truck right here) Transmission: 6-speed w/ 4 wheel drive Gears: 3.42 Miles on truck: ~53k Miles driven on tune: ~3k Performance Mods: None, apart from the tune of course Other mods: bed cover, remote start, tailgate damper Tuner: Diablo Intune I2 Truck role: Getting to/from work and doing work. Have another car for long trips Background I purchased a Diablosport Intune I2 for my previous vehicle, 08 Colorado I5. The tuner for that truck was the best investment I ever made, especially for the transmission tune. Lightning-quick shifts, more power, better throttle response, no complaints. That truck has since left my life, needed something with more payload, in comes the Sierra... Intro The truck commutes 15 miles per day for work and is otherwise a weekend warrior. About 80% city, 20% highway driving. Had no complaints with how the truck drove, until I started noticing an occasional downshift "clunk" when going around corners between 20-30 mph. Then, I remembered how awesome the I2 made my Colorado transmission. Said, "Screw it, lets tune this thing and see if the problem goes away and if I can improve shift quality." So I purchase the extra license for my I2, install the canned 87 octane/firm shift tunes, and go out for a drive... Big mistake. The canned transmission tune was QUITE bad. Started investigating, lots of complaints on the Diablosport forums, only solution is to try a Diablew tune. So, $150 and 3k miles later, here we are! The Process Contact Diablew with your information, wait 5 seconds for him to respond, pay the man, follow the instructions, profit (for him... and you, eventually). Don't want to cover this too much as it's not that interesting. Onto the tune! The Tune One engine and one transmission tune provided with tweaks available upon request. The engine tune can be provided for the octane of your choice, but keep in mind that the 87 and 89 octane tunes are the same with no spark advance provided for 89 (ie. might as well run 87 unless you tow in high temps, or just request the 91+ tune). The engine tune, after driving 150-ish miles... wow, I like it. Noticeable power increase in the low end (around 1.5k rpms). Feels better across the board. On the stock tune, I was getting random blips of knock retard on mobil gas, even 89 octane. The Diablew engine tune has yet to register ANY knock retard on 87 mobil. Better for the engine, more power, can't complain. The V4 mode was also disabled, though I did not have an issue with V4 (part of the "Cannot notice it's even working" club, which only has 7 or so members on this forum). MPGs are about the same, pedal feel is spot-on, spins the tires too easily (not a complaint, unless its raining) The transmission tune, on the other hand... it's not bad, but not for me. This was the primary reason why I wanted to tune in the first place, but I am a bit disappointed as a transmission tune made my Colorado (by comparison) FAR better than stock. The tuned transmission on this truck shifts a tad later (which I felt wasn't necessary) and also *tries* to shift firmer. I say "tries" because the firmness is random. When the transmission tune shifts firmly across all gears, I love it. But, the inconsistency breaks it for me. It also does NOT shift faster than stock, or at least not noticeably so. After searching through tune forum posts for this truck, it seems like everyone has had a different experience and probably no fault to Lew as a tuner, just that the truck has a silly transmission. No improvements after 3k miles of driving on this transmission tune, either. Remember that downshift clunk when taking turns around 20-30 mph? Since the transmission now shifts harder, the flaws are more pronounced. I reverted back to stock and due to the additional engine power in the low end, I think it makes the stock tune that much better. Due to the higher shift points, I feel that this tune would make more sense for a truck with the 3.08 gears (vs. my 3.42) as many people with 3.08's seem to hate the shift points. The tune is worth a shot no matter what, but my truck did not like it, unfortunately. Final thoughts Want more power for only a few hundred clams? Get a Diablewtune. More power than the canned tunes, less knock retard, and will take advantage of engine mods. Certainly try the transmission tune as "your mileage may vary" (har har), but the engine tune alone was worth it. Estimated gains from Lew are 12-39 HP, 10-35 lb-ft of torque, and +0-3 mpgs (all of which are mod dependent). Since I have no mods, I am happy with an additional 12HP/10lb-ft. Feel free to ask any questions!
I agree, they only say "It is what it is, deal with it" which isn't very informative. My only understanding of this comes from my background as a mechanical engineer, but I cannot speak for GM! I'm only assuming from my experience with the industry that GM had engineers run an analysis on the bevel gear teeth contact under certain loads (such as a fixed tow weight) and determined that too much heat/stress was generated with the 3.08 vs. the 3.42 gears, therefore reducing tow capacity for the 3.08 no matter what engine is powering it. Less or smaller gear teeth contact with more engine torque can increase stress on the teeth. The 5.3L can probably tow more with the 3.08, but GM needs to cover their butts depending on what their engineers say for warranty purposes I'd assume. Some interesting information would be throwing the 6.2L into the mix. If the 6.2L has the 3.08 rear and still has a super-low tow capacity, we can probably assume the gears are the limiting factor. I can't imagine that the 6.2L would have those gears, but now i'm curious...
Rear-end torque doesn't necessarily matter as much if the 3.08 cannot handle the same towing stresses as the 3.42. So, to answer the question of the first post, that's how GM states the V6 with the 3.42 can tow more than the 5.3L with the 3.08. Both engines can obviously tow more, but when the 3.08 heats up more under higher loads increasing chance of failure, they reduce the max towing recommendation (regardless of engine) Edit: It's a material composition problem of the rear axles (3.08 vs 3.42). The 3.08 under higher loads will heat up more, degrade fluid faster, and break "teeth" sooner than the 3.42 under similar circumstances. Another way to think of it is that under equal loads, each tooth of the 3.08 will see more stress than the 3.42 and has a higher risk of failing sooner. Therefore, GM engineers determined the 3.08 rear axle as the limiting factor (fails first) and lowered the max tow rating to cover their butts.
The 3.08 rear end is simply not designed for towing more and is the limiting factor, mechanically.
My MPG's dropped when I installed the Diablo MPG tune with a Diablo TCM tune (either firm or hard shifts). Returning the TCM tune to stock fixed this. I hated the canned Diablo TCM tune anyways. Did you apply a Diablo TCM tune by any chance?
I'm also curious about the high mileage maintenance and any common problems. Seems like a valve cleaning would be nice at 100k miles At 80k miles, I agree with you getting some new fluids in the differential, maybe on the transmission (if the fluid looks bad). Who knows what the previous owner did, the peace of mind will help in the long term. Oh, brake fluid flush! The fluid is supposed to be clear (easy to check). If it's brown, get it flushed to prevent rusty brake lines. Check again in another 50k miles or 3 years. 2014 Maintenance Schedule
Hey OP. I, too, came from a Colorado (2008). Loved that truck. Unfortunately, it had some pretty serious issues at around 90k miles (Valves not seating properly, new cylinder head). I got that fixed and got a diablo tune. Holy cow, made that truck even better. Lightning quick shifts, more power, couldn't go wrong. Recently purchased a 2014 Sierra Work Truck w/50k miles. Apart from the lack of auto mirrors, it has all the same features of my old truck and was dirt cheap, so I cant complain. Love the power and ride quality, though I do notice a slight shimmy at speeds greater than 75 mph. Smooths out with a little weight in the back, however. What bugs me the most with this truck is the transmission. I have a Diablew tune and was expecting the results I had with the Colorado. While the shift quality and speed is a little better than stock, it still lags when you want to simply pass on the highway and need to downshift one gear. I may need to adjust to it... Regardless, when I drive like a normal person, no complaints with the transmission. I too hope to drive this thing for as long as possible!
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EDIT: Just got off the phone with my local GMC dealership service center. Stated that shaking at speeds in excess of 75+ mph has been found to be the nature of the fully boxed frame unloaded. He told me he drives a 2015 Sierra 1500 with the same symptoms and searched high and low for a solution when he first got the truck. Found out that placing weight in the back resolves the issue. Has anyone tried this? ORIGINAL MESSAGE: 2014 Sierra 1500 5.3L 4x4 3.42 w/ 49,500 miles Jeeze. Just got my truck a few weeks ago and noticed the shake at speeds in excess of 75mph. Lots of pages on this topic, lots of reading! So far, the only solutions I can find are: Driveshaft balance Spring clamps New shocks (Rear only? Seems to only cover the actual problem) Torque converter (seems to apply to the 8-speed only) I may be missing a few others, but I would love some sort of sticky that summarizes the solutions that have worked, and which engine/transmission/axle combinations it works for. Feel free to PM me your year, engine, drive train, transmission, and axle because I wouldn't mind compiling this info for everyone. Almost at 800 pages of information here, there must be a solution.
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