Hello group, i have a 2002 GMC Sierra 4.8 tecently my truck will raise the rpm when I’m slowing down using breaks. It usually goes up about 2-3rpm higher just as soon as I step on break. Is it a bad brake booster?

 

2-3 rpm or 2-300 rpm? 2-3000?

2-3 is nothing. Fluctuates more than that at idle if you have a bad tune lol

 

More than likely the transmission just downshifting as you decelerate.

 

Clamp off the booster hose with a pair of vice grips then test (BE CAREFUL)

 

It doesn’t matter the speed it does it at 15-65 mph.

 

That’s the torque converter unlocking

 

This happened to me once and it was the floor mat sitting on top of the pedal.