Gryphon problem.

[04FX4]

I have noticed when driving real slow under 30 k my truck will hunt. It goes from 800rpm -1300rpm constantly and will not stop unless I let up on the gas pedal. Any thoughts? I also was wondering how much more HP a 2006 F150 has then my 04. The reason I ask is I know a guy who has the same truck as mine 2 years newer and no mods, and we have tried to see who's truck is faster. We start off the line about the same and eventually he pulls away from me, I would have thought I would have had the upper hand. He is running 87 fuel no nothing just stock. My truck has only 35000k his 58000 both are FX4 Screw same engine same everything, even same color,I cant figure this out.