Engine hesitates when hot at full throttle

Whell the problem im having is whit my f150 4x2 6cyl 4.2l 5 speed manual.

When the car is started cold, theres no problems at aceleration or lack of power. But when it has bee running for a while (30 min in stop and go traffic) the engine hessitates when you fully press the gas pedal. Desent mather the speed or the gear.

There are no codes in the truck. When in neutral, i have done the followyng test. Whit the truck hot, i fully press the gas pedal, the engine accelerates and starts hessiteting at 3000rpm. It dosent go higer, BUT, if i back off the gas pedal to 1/2 or less, the engine accelerates up to 6000rpm (the max marked it the cluster of this truck)

What could it possibly be? I really have no clue why it only happens when is hot....

(It acts exactly like the old two barrels carburetors, when you fully press the gas pedal and the high speed jet is cloged, somebody remember?)


P.S. This same problem happen to me about 2 year ago. I remplaced the fuel filter, clened the MAF, changed the air filter but the problem didnt go away. Then, about 1 month later using the truck whit this problem it suddently fixed itself. Never happen again until now.

Thanks