My 99 was doing the same thing and I read in another forum to take the throttle postion sensor off and clean the hell out of it with starter fluid and work the mechianism while your doing it. I did it and I took and 200 mi trip this past weekend and it only did it once. Do a search for it (TPS) I did that and adjusted my TV cable just a bit for more line pressure and a slight change in shifting. reset the computer and she drives like a different truck. clean or replace the TPS first and see if that fixes it.