Last night i had to take a cruise up to my uncles cabin to fix a few things. On the way there doing around 75 my truck started to cut out and sputter for a second every once in a while. on my way home it started to get worse then got real bad. It would cut out in the higher rpm at first then it started to cut out everywhere. On the highway i would rev up to about 1500rpm and then stay there and sputter everyonce in a while. With the clutch in i could rev it up, but in gear i could only really get 1500rpm out of it. Also if i kept the clutch in and coasted down a hill at idle for a little it would rev up for a few seconds then go right back down to 1500rpm and stay there until i did it again. I was worried it was the lift pump going so i got it home asap giving it as little throttle as i could so i could avoid ruining the IP. Well today i started it up and was going to take a quick lap around the block with my dad to show him what was happening, but it was fine. We drove for about 20mins and it was perfect. Any ideas? Could it still be the lift pump?