blckblt

Are all your fuses seated tightly? Ubec bolts for the fuse block tight? https://gm-techlink.com/?p=13437 When I had my 2020 TB I had the same thing happen. All of the fuses in the panel seemed to be loose. I was able to press each on in a few mm. After that truck started right up. I made an appt at the dealer and they didn't find any codes. The Ubec bolts were fine (green indicator was up) but they still checked everything in the TSB and retightened etc. I had the truck for at least 6 months after the dealer looked at it and didn't have the issue again. While your codes aren't listed it could be the cause.

Did you reset the computer (trip and 25/50/400 mile)? Trucks get a lot of idle time before they are purchased.

Out of all three options from GM I would only go with the 10 speed.

Sounds like your dealer lost or gave your supplemental manual to someone else and wants you to pay for replacing it..... You should get all of the paper manuals with your truck for FREE.

When I had my 6.2 I tried to run 93 if not then 91. I did notice slightly better performance and higher MPG.

Here is a pic of my MX4

I have a BAK MX4 folding and mine are exposed. https://bakindustries.com/bakflip-mx4 They show one of their rolling covers on an AT4. https://bakindustries.com/rolling-covers

The oil visually looks good? Doesn't look like it is mixed with coolant? Def. an odd problem. I haven't heard or seen that before.

I had the USB ports and SD card reader stop working in the center console in my 21 AT4. This was after 3 days of owning. The connector had come undone behind the dash. Probably wasn't secure from the factory. You could check all your fuses and make sure that isn't the problem. When I had my 2020 TB it died in the parking lot at my business and almost all of the fuses were loose. after pressing them all tight into their sockets the truck was fine. dealer couldn't find any thing wrong. they also checked the ubec bolts but they were good too. ran fine for 6 months after that....

I have had my AT4 for almost 2 months. I use the MF tailgate multiple times a week. Just being able to drop the inner gate is helpful for loading and unloading stuff in the bed. The step is nice as well. I haven't used it in the load stop positions yet. I don't leave a hitch in as I don't like the look, don't want it to rust to the receiver and I value my shins. I also don't tow very often. If you are loading stuff into the bed with ramps make sure you read the manual. Either need to lower inner gate or distribute load across whole tailgate (manual explains better). The MF tailgate will not power close. I thought the MF tailgate was a gimmick until I used one.

That is good on the weight, I would have thought more. I will be getting black AT4 and GMC badges in a couple weeks and deleting the chrome Sierra on mine. The chevrolet done in black or another color really make it pop, especially on white.

I drive a truck as I like trucks, I am not a car guy. I like to be in a bigger and higher up vehicle as there are a lot of shitty drivers. With that said I do use my truck as well for truck stuff so if I can get better economy it is an extra benefit for me. The response of no one drives a truck for fuel economy is not helpful on a thread asking about going from the 6.2 to the 3.0 as fuel economy would be the main reason for doing so......

black badges and black chevrolet for the tailgate. To me the chrome blends in too much with the white. I am not a fan of chrome though How much weight did those bumpers add?

Trim and tires effect this. Non AT4 and especially non Duratracs would give about 2-3 more mpg. Those 2 items add a lot of wind drag and rolling weight for the tires. With that said I am a direct comparison as my TB had duratracs as well. I will add that my lifetime went up to 22.4 yesterday with basically just small town driving yesterday. I will add that I drove my 6.2 like it deserved to be drove at times. That motor was fun. As the 3.0 is just getting broken in I have started to get on the pedal heavier. Regardless my lifetime right now is slightly more than a 7 mpg gain. Diesel around here is the same (or cheaper) than premium. 160-170 extra miles per tank. Roughly saving me $20-25 per tank. I believe that the silverado gets slightly better MPG as it is a little more aerodynamic. I will also add that the 10sp transmission is a game changer. smooth. always seems to be in the right gear. definitely helps with the economy. I have had 6 and 8 sp GM transmissions, tundra 6 sp, ram 8 sp and by far the 10 speed is the best 1/2 ton transmission I have driven. I am curious to see what 14k of mileage looks like on the 3.0 for more accurate comparison.

These are the ones I got: 84742428 https://accessories.gmc.com/product/crew-cab-sport-step-assist-steps-in-black-with-sierra-script-84742428?year=2021&make=GMC&model=Sierra 1500&modelId=548&body=Crew Cab Pickup&bodyId=22&wheel=Short Box&wheelId=651&trim=AT4&trimId=5102&drive=4WD&driveId=8&engine=3.0L L6 DIESEL&engineId=17881&bodyNumDoors=5&categoryId=12062 GMC accessory page calls them sport steps however when you go through the build site they are listed as Off-Road. The high clearance steps are too high and narrow for my son to use. I had the off road steps on my TB so I knew my son would be able to use them.

2020 TB w/ 6.2 to 2021 AT4 with 3.0. Had 14k miles on 6.2 over 15 months in Maine. Lifetime of 14.9 MPG. Small city driving, some rural roads and some highway. I have a ~35 mile trip that I make 3 times week. The best I got was 21 on trip and typically 19ish. Mix of all conditions except highway. 2021 AT4. 1100 miles. Lifetime 22.3 and has been climbing. Same driving as above with the exception of cold winter as I got the truck in mid April. On the same ~35 mile trip as above I average 25-31. Depends on traffic, lights etc. Last night I got 27 and the truck did a regen. Prior to that I hit 31 on the trip before. Having all the torque at 1500 rpm is awesome. I loaded the truck with bags of mulch (31 bags) and didn't even notice the weight (truck squatted 3")

My cardinal red 2021 AT4 w/ the 3.0. Offroad steps and bakindustries MX4. Black exhaust outlets. Will be swapping to black GMC emblems, black AT4 emblems and will debadge the chrome sierra on the tailgate next month with I get the front windows tinted. 1100 miles. 22.3 lifetime mpg (idle, city, country roads, highway mix). This has been going up over the past week. I have a trip that I make 3 times a week ~35 miles round trip. 25-31 MPG depending on traffic, lights and regen (got 27 last night and the truck did a regen during). With my previous TB w/ 6.2 the best I got was 21, typically 19ish on the same trip.

Basically yes. However there are some features that were oddly left off the TB trucks. I had a 2020 TB with every package you could get. I didn't have auto dimming rear mirror, power folding side mirrors. Those options were standard on the 2021 AT4 that I bought. my 2009 LT chevy 1500 had those features..... AT4 gains Driver Alert 2, tech package, carbon pro as packages.

There was a shortage of all running boards a few months ago (early Feb). My AT4 order had to be cancelled as it would not ship with the premium package or with the offroad running boards that I swapped from the package. I had to order the truck with the value package (everything in premium minus the high clearance step). Once the truck came in (about 4 weeks ago) I was able to order the offroad steps and add them to the truck at the dealership. I would guess that if you ordered with the premium package and your truck has shipped you should have them already installed.

Unless you recalibrate the speedometer the computer will not read MPH right and mileage driven will be wrong. With those being wrong MPG numbers from the DIC will be wrong. You must 100% hand calculate with miles driven by GPS or an APP (waze etc) and then use gallons off the pump.

AT4 and the Trailboss don't have the front air damn. Improves ground clearance and approach angle for what GM considers to be their off road 1/2 ton truck. You can probably add it. It might improve your MPG a little if you do.

I would assume you checked both glove boxes, the center console and any other storage compartment? I had a similar thing with my 2020 and un-known to me my son had put a golf ball in my center console. He likes to hide things on me and play tricks....

No matter what truck you get I would strongly recommend the 10 speed transmission. I just went from the 6.2 to the 3.0. I loved the fun power of the 6.2 but the 3.0 is amazing and can easily get 25-30 mpg (I have an AT4 with the duratracs).

Did you get recalibrate you speedometer? If not you will need to hand calculate and get the miles driven by GPS/app as your computer will be off.

Both on mine.