Does anyone know what could be wrong with a 2.9 litre 5 speed that really hesitates on acceleration? Could it be the fuel injectors or the fuel filter? I have used 93 octane gas and also tried the fuel additive. It works for a while but then goes back to the hesitation and sometimes back fires. For the most part it is when I shift into 4th gear and try to accelerate. It sounds like spark knock. I have had the truck checked out not too long ago - replaced belts, hoses and filters. I am not sure they changed the fuel filter though. I have had someone mention trash in the lines but I don't know how to fix that. I would appreciate any suggestions.