Gary, I dunno how much help this is gonna be but I'll tell you what I've seen that I think is somewhat similar; on my 02 2500 with the Cummins Diesel it would run poorly until warmed up, with poor acceleration/power. That problem got worse and worse but when it first started happening it was just a limited power problem shortly after startup and under acceleration. Since we not only have completely different vehicles (yours, the new body style, mine, the old body style; yours gas, mine diesel), it wouldn't hurt to check the fuel pressure at your fuel rail (as opposed to checking mine at the injector pump) to see if it might be a bit low. You could simply hook up a fuel pressure gauge to the test port on the fuel rail and then run it out to the windshield and duct tape it there and shut the hood and then drive it under your specific condtions and see if the fuel pressure is in the proper range. I don't know where it should be on your truck but a figure that jumps to mind is around 40-50 PSI for fuel-injected gasoline engines (as evidenced by my 1998 Dodge 1500 360 C.I. and my
1990 Corvette 350 C.I.). You could buy a factory service manual (HIGHLY recommended if you plan to keep the truck for any length of time at all, even if you normally don't mechanic on your own stuff (just so you can kind of keep track of what the service guys are telling you)) and find out what the correct rail pressure is (or buy a Haynes manual, lots cheaper) or ask the service guys at the dealership if you trust them to tell you the truth.
Another thing, and this may sound like I'm on crack but I promise I'm not, my dad's 1998 Dodge 1500 360 C.I. (yes, the same one I mentioned above, when I got rid of it I sold it to my dad) with 122,000 miles on it was running like hell; at startup it would try to die and he was having to use the foot-feed at startup, something you're not supposed to do on a fuel injected vehicle, as I remember from the days when we went from carburated vehicles to fuel injected vehicles). I talked to a mechanic friend of mine and he suggested cleaning out the throttle body (dunno if that's the technical term for it, but it's basically what it is; below the air cleaner there is a body that has one or more (two on my dad's/my old truck) butterfly valves). I used an old toothbrush and some carb and choke cleaner (the cheap stuff from Wal-mart and I hosed that thing down and scrubbed around the inside of the housing, particularly hosing down the areas that looked like they lead to sensors. It took some effort to get it to start after that (my buddy told me the carb and choke sprays would make the engine hard to start the first time after I did it) but once it started it ran beautifully and my dad claims that now it not only runs better but seems to have more power. There was definitely a lot of soot build up (lots of black gunk built up) in the throttle body and I cleaned it out pretty well; I dunno how that made a difference, maybe a dirty sensor, maybe restricted airflow (the butterflies shut so tightly that I could spray a puddle of carb and choke cleaner on top and it would sit there for a bit before draining (or maybe evaporating, away)), but it made a huge difference from what little I saw myself and what my dad tells me.
In any case, I'm not sure this'll help you but it should all be some things that you can easily check/do yourself and not cost you any money (other than the carb and choke cleaner and the shop manual (which I really do think is worth its weight in gold)).
HTH. YMMV.
Please let us know when you find the problem and again when you find the solution.
--HC