the reason i say that is because back in the day i had a similiar experience with my truck. truck ran like a top until i installed gov springs. then after the install it still ran pretty good but in neutral it would break up around 3k rpms. a .060 tork tek OFV and a raptor fuel pump and it has never stumpled at any RPM again. i always install gov springs all the way tight. you normally can get 6 clicks with initial.