My little brother has a 95 F150 4X4 extended cab with the 5.8. Last week he put a set of shorty headers on the truck. The headers were Pace Setter headers. Install went smooth. He bypassed the air pump and did not re-install it. Also the cats were making noise due to the inside material breaking up so he cut them open and cleaned them out. Before this work the truck ran like a top. After the work the truck still runs fine but it shifts harder than any truck we have ever even put a shift kit in. It will literally throw you around now. I know this cannot be healthy for the truck. I am looking for any ideas as to what may be causing it or what to maybe look for.

Thanks for all the help in advance.