I have a 1995 F-150 4.9 l engine with a standard transmission. I am having problems with the engine hesitating. The engine idles fine but when you put the engine under load I have to rev the engine higher in order to take off. Also most of the time I have to drive in 3rd gear because when I put the truck into 4th gear it bucks so bad that I have to downshift to 3rd. Any suggestions I have changed fuel pumps computer and just about every sensor in the truck but still having the hesitation problem. help