A guy I know has a problem with his fuel. he can fill up his tank and run it dry then it'll die of course. here's the kicker, when he is towing his four wheeler and the fuel gets to 1/4 tank it spits and sputters and dies. now the four wheeler and trailer don't weight that much so it's not making the rear end drop hardly at all. he has put in additives to get rid of any water that might cause it, but if there was water in the tank it would happen when he gets low on fuel any ways.. any and all ideas would be greatful.

note: he has a 04 with the 5.4