so yesterday my truck started loping. some time it isn't enough to really notice but other times the tac is jumping between 500 and 350 rpm. so today I change the fuel filter and the heater pre screen, the overflow valve is only a month old. Any ideas or people who have experienced this please HELP. thanks

 

check for air leaks at the pre heater. just in front of the stock lift pump. 500 idle is far too low. you need to bump that up to 750-800. is your new OFV a quality unit?