2003 Reduced Power Light / check engine problem

[stageone]

The truck starts fine and will sit and run perfect. But sometimes while driving the check engine and reduced power light come on and the truck only wants to go about 20 - 30 mph. If I shift it down to 1st it will gain speed and I can shift myself thru the gears and get it going as fast as highway speeds. So I took my cheapie scanner (a sweet Actron CP9135) out with me for a ride when it coded and fell on it's face I cleared the codes as I was still moving and the second it finished clearing the codes and the lights went out it took right off, full power. But the codes keep coming back within seconds. As many time as I liked I could clear all and I got the same result. So I parked it with the key on engine off ran the scan and got the following codes:

1221, 1271, 1633, two times each so my scanner said it had 6 codes. Also the description for each code is the same, "manufacturer specific DTC"

After clearing the codes I started the truck and it ran perfect while in park. So I let it sit and run without moving for about 20 min. Then I put it in reverse and move it backward and then held the brake to give it some load. Still fine. Shift to neutral, fine. BUT the very second I shift to drive it codes and goes to reduced power with that and the check engine light on. So I did it several times and it is the same each time. As soon as it clicks into drive it codes.

I really do not have a clue where to start as the codes tell me little more then the numbers and that they are “manufacturer specific DTC” and that is all. Any thought or info on the codes would be hugely appreciated. I hope this is not the start of a terrible ordeal. I’m in to position at this point to take it to the dealer so it on me.

Thanks in advance for the help.

[maxwedge]

These codes refer to the position /correlation of the tps on the gas pedal and how the motor that opens the throttle responds to the tps/pcm commands , this can be a wiring or component problem in one or both of these controls.