My '91 has been difficult to start when the engine is warm and the ambient temperature is warm. Vehicle starts great when it is cold. Runs fine all the time. Yet the warmer it is outside, the tougher it is to start after it has been shut off. The engine cranks at normal speed but struggles to start with out several long cranks. It has a stock 302 with 120K. Plugs, cap/rotor and fuel filter have been changed over the last year or so. I've had the truck for about 6 years. It has at times been difficult to start when warm, but is much worse now. Spring weather is right around the corner. Any suggestions?? Thanks in advance!