1985 f250 with the 460 at night when its nice and cool out it runs like a dream. During the day with it being a little hotter outside on acceleration it lacks power it sputters and stutters if I let off the throttle and get back on it a little it will jump forward like it wants to go but it will loose power then jump forward again and keep doing that until I give it more gas or let off. it seems the more I try to accelerate the slower it goes