2020 sierra 1500 at4 3.0 concerns

Sawyer · 2026-10-24T21:23:00-0500

i recently bought a 2020 gmc sierra 1500 at4 with the 3.0 (first diesel ive ever owned) only reason i bought was because it was a steal. 127k miles for $23,000. the dealership replaced the TCM and the def injector (said it was 79% bad) after driving it today i noticed that it feels like its jerking when shifting out of first or second gear. drives perfect after that its just the initial starting from a dead stop when it does it. every now and then i notice that it doesnt do it quite as bad. please tell me im freaking out for no reason really...?

also the front right fog light is out. from what little research ive done you cant just replace the bulb but instead have to replace the entire lighting assembly? is this true?

thanks for any help

R467X · 2026-10-24T22:42:32-0500

Probably your valve body. Has the truck ever had a transmission service done? I would start there. That is a lot of miles on a 1500 and don't be surprised if you find yourself with a new transmission sooner or later.

gemarsh · 2026-10-25T02:29:59-0500

Welcome.

Any history of the oil pump belt being replaced?

gm recommends the belt to be replaced at 150k miles on the LM2 and 200k on the LZ0. Same part number, same belt. I'm running mine to 200k if we get the '21 that far.