Weird miss after third gear

Tyler Bruder · April 22, 2020

I have a 2008 gmc 2500hd with the 6.0. Now I've done a lot of work to it but something happened recently and I cant figure out what is going on. I have no check engine light and itll drive but once I get to high rpm in 3rd gear then shift to 4th (and 5th and 6th) it start missing really really bad. I lose all speed and all power. I had my computer hooked to it the other day just to see the codes (when it starts missing check engine flashes then when I come to a stop it goes away) all the code gave me a a random multiple miss fire. I have about 150k on it. Did plugs coils and all that at 100k. Does anyone have any ideas?

davester · April 22, 2020

maybe fuel pressure, knock sensors, injectors, plugs, coils, wires (50k is enough that it's possible somethings gone wrong with them).

Formulabruce · April 22, 2020

The air intake , pull ff the big hose to the TB and clean that whole area Very well. Both sides of the throttle plate with THROTTLE BODY CLEANER, ONLY.

I am sure your truck needs it if it has not been done. It can cause some issues. Good luck!