i got a 96 chevy that has 164k on it its a vortec v6 with a 5spd. well before i did a tune up about 2500 in 4th gear it would spit and sputter and like power lost was notice able but if u gave it more gas it would clear up but i know that it has a 160 thermostat in it and cat has been gutted but has never done this before even when my buddy had it because i use to borrow the truck all the time but after i did the tune it this happens every once in awhile.