Ok, '84 F250, 2WD, 6.9idi, T19... New front tank, sending unit, switch valve blown out with air... Everything copasetic during normal driving around town, or hiway...however, if I put my foot to the floor after getting into 4th (around 25mph or so)...after a bit, I will get some hesitation and surging...happens on either tank...goes away after a bit of normal driving at hiway speeds. Usually do not go all the way to the floor when accelerating... So...what's the consensus here...fuel lift pump, or IP...or both. Thinking on doing the lift pump first and see it the issue goes away. Less $$ too...IP is a spendy proposition...'specially on a fifteen hundred dollar "go to the dump" truck. Do not want to get stuck with a load of crap on the way to the dump however... Thx for the replies!!!