I have a 94 F-150 with 83k miles on it. When I am at a complete stop and hit the gas the engine hesitates and seems to struggle for a bit, the lighter I touch the gas pedal the more it hesitates, it even stalled on me once in a fast food line when I just tapped it to move forward a bit. There is no other problems with the truck, it runs wonderful and I got it up to 75mph on the highway and it is smooth as can be. Is this anything serious? What can I do to correct the problem.