I can't give you a proper technical answer for why your tranny is hunting at that speed..........odd
I'm sure Jack or Bill will figure that out for you but you may have to give more detail as to exactly what's happening.
As far as 04 vs. 06..........same horsepower and torque. Here's an important question for you though. Is your truck Canadian or American?......and what size are your wheels?
If your truck is Can. and you have 20" wheels........you automatically get a 3.55 gear ratio with 20" wheels!
If he only has 18" wheels.....then he would have a 3.73 gear ratio........and Yes - if you raced he would cover you with ease!
If this isn't the case......I have no explanation other than variation from truck to truck. But if both have 18" wheels and 3.73's and you are tuned and he isn't........something is really friggen wrong!