I just replaced exhaust manifold gasket and now my truck is quiet but it runs worse !! I have no power when I accelerate and it doesn’t switch gears properly high Rpms then shift hard also backfiring while accelerating but in idle sounds okay the scanner is giving me P0101 ,0102 , 0300 . Changed the plugs and wires also changed the mass airflow sensor and that did nothing !! I’m very aggravated and could use some help

 

runs worse...means what. describe symptoms that describe what is happening..ie no power, misfires

 

Sorry for not being more in depth . I edit my post hope this will help

 

Sounds like a plugged catalytic converter.

 

yep +1. a clogged cat can blow out the exhaust manifold gaskets. remove the pre cat 02 sensors from the exhaust pipe to bypass the cats...it will be loud but if the power returns and the misfires gone...you need new cats.
if air can't flow out, it can't flow in ...this sets the maf code.