Another JR

Is your truck not available for you to look? If not, can look at mine later this morning and post back. I suspect they are easily accessible.

Newdude posted while I was typing. If they didn’t have very good torque control with their impact driver or if they did the final quarter turn after applying 89 ft lbs, I agree with him they should be replaced.

Based on the service manual picture you posted, the four vertical bolts are single use and the torque specifications appear to be intended to be “torque to yield,” which permanently elongates the bolt. If they were torqued per that specification they should not be reused. However, if they used a properly limited impact device and only torqued them to the initial torque value of 89 ft lbs and did not do the final 70 to 80 degrees of additional rotation, they never yielded the bolts and they could be “reused” and torqued properly. The biggest issue in deciding whether to reuse them likely will be uncertainty over the torque applied by the impact driver.

Why the extreme lift?

The dealer I bought my truck from is actually pretty good. The problem is the labor force issues due to the dealer industry practices. They are struggling to keep experienced mechanics due to the pay structure, and the fluid change staff is minimum wage and uncertified. I still work with them when I need to, but I have had issues due to incompetence or lack of care as I described above. The unauthorized software update issue I suspect is driven by GM policy, but it is still an issue. It is my goddamn truck once i take delivery. You don’t modify it without my permission.

I view every visit to the dealer’s service department has a significant risk that they will do something wrong, use the wrong fluid, or change software without permission. Sometimes it’s unavoidable, and usually everything is fine (other than you never know what fluids they used), but I definitely try to minimize my exposure by doing everything I can on my own. I make them put on the work order that software is not to be updated without documented permission from me. Definitely inspect their work after fluid changes for loose plugs and filters, and incorrect levels. I have had all of these things happen over the years. I even had a dealer leave a connector disconnected after a minor fuel vent system filter recall on my Chevy Volt that bricked the car on the freeway when the lithium battery was depleted and the gas motor should have taken over. In another case, a friend coming over for dinner arrived at my house and I pointed out the trail (not drops) of oil behind his truck and noted oil still pouring out under the truck. He had just had his oil changed at the dealer and drove 20 miles to my house. We followed the trail back and found his oil drain plug a half block back along the road. If it had fallen out a mile sooner he would have gotten the red light and may have ruined his engine.

It is always a good idea to exercise it at least every few months to make sure the actuators don’t get stuck. It is also a good idea to actually drive it for at least a few hundred feet when you do that so seals experience motion and oil movement. Off pavement or snow/ice is best for this, but driving wet pavement in a straight line for a short distance will work if you don’t have other options. I have forgotten and gone as long as six months between exercising it on my 2021 and it has always shifted promptly. I usually just use my straight 300 foot gravel driveway.

The 6L90 in the 2020+ trucks has several improvements over the 6L90 in other trucks, so the comments made about issues with previous versions may not apply. I have been totally happy with the 6L90 in my 2021 3500 HD. The L8T has plenty of torque over a wide speed range and does not need to be held in a narrow rpm range unless you are towing near the maximum weight. Even then, six gears works just fine. Personally I don’t like what i consider the excessive shifting of most ten speeds, but i have not towed with one of these trucks with a ten speed. If you are buying used I would prioritize condition, miles, maintenance records, absence of stupid unreversible modifications, and towing history as more important than ten speed versus six speed. Make sure you try the seats out before choosing a trim level. I can drive my SLT with the leather bucket seat (premium pkg) option for 8 hours and get out feeling fine. I was uncomfortable in the SLE cloth seats with fold down center seat by the end of a 20 minute test drive. My wife loves the SLT leather bucket seats, too.

I have no first-hand knowledge about it but I have seen quite a few comments that GM selected lower viscosity gear oils to slightly improve fuel mileage. Personally, I care more about longevity and reliability than fuel mileage on this type of vehicle, and I have not read any cautions about using 75w90 in place of the 75w85 specified for the front differential, so I went with the 75w90 I have used for 35 years on other GM trucks and SUVs.

Because it has never used much oil, I haven’t monitored it closely enough to know for sure. However, the measured drop on my latest longer interval after our road trip of 4500 miles (nearly 0.6 quarts) was roughly proportional to the drop in previous 3750 miles intervals (a little less than 0.5 quarts), which would imply the drop is steady.

I received my truck with 2 miles on it and no other customer test drives, and I followed the break in carefully. I may just have been lucky though. My truck loses just under a pint in my 3750 mile oil changes intervals based on measuring added versus drained through 5 intervals now. I can’t ask for much better than that.

Also, I have noticed that prolonged high speed highway driving under some load (slide in camper wind resistance) seems to use a little more oil than general lower speed driving. This is for a 2021 with 19k miles that uses almost no oil between 3750 mile oil changes with Mobil One. It is based on my oil changes measurements after a 4000 mile Southwest parks trip this Spring.

Here are pictures of the specific Amsoil product I ordered (GL-5). The price was about $17.25 per quart plus a $10 six month membership fee. Shipping was free because the order exceeded $100 for six quarts. Valvoline in my local stores was around $18.

I changed the fluid in the rear axle of my 2021 gas 3500 hd last Fall at 15k miles. I used Amsoil Severe Gear 75w-90 in the squeeze packs. GM specifies slightly different oil viscosity ratings for the front and rear differentials for fuel mileage reasons, but 75w-90 is acceptable for both. Amsoil wasn’t any more expensive than other products on the store shelves. I did the short term membership deal and ordered 6 quarts to get free shipping. I don’t plan to change the front fluid until 30k. I removed the cover and wiped the inside of the cover and the differential housing as well as I could. It took 3.5 quarts to fill it to 0.4 inches below the bottom of the fill port. No additive is needed with the proper fluid type. I have 5000 miles since the change including some off pavement driving and the G80 locker behaves normally.

I have consistently gotten 7-8 years out of the batteries I have bought from the Chevy dealer parts department, and their prices are competitive if not better given the performance of the batteries.