stumbling at idle 2003 4.8....TPS sensor problems?

[JeRM82]

I have a friend who just bought a 120K mile 2003 silverado with a 4.8 in it. It has a problem when it's idling where it almost dies when you put the trans into reverse, and it you hold the brake and BARLEY toutch the gas pedal enough to get a response....it stumbles down to 400rpm, and JUST about dies....but comes back to idle....my friend says that it HAS dies on him like that before....but we are still trying to figure out EXACTLY the same conditions other than what I just said....I used my Predator and scanned the Throttle Position at idle, and its at 15% while at IDLE......and "arbritrary (I think) throttle position" is at the same, or just as high at 14.xxx% at idle.....Is that a BAD Electronic Throttle control or Throttle position sensor?
I scanned my 07 5.3 truck and at idle and durring the same put into reverse conditions my truck sits at only 5%, and bumps up to 6% or so when I put it into reverse, or tap the gas like I was doing with his truck....BOTH of our trucks idle at around 500rpms or so....his almost dies and doesnt seem to be compensating for the load put onto the motor by putting the truck into reverse.....
It SEEMS like its a TPS sensor or that electronic throttle control because the truck at IDLE sits at 15% Throttle position......its like THREE times as high as mine is...and it STILL idles at 500 rpm's......anyone ever run into this before? I am going to do the idle reset from the sticky above this thread and clean out the Idle Control Valve thing...ha ha....but while I was doing that I thought I would get some input from you guys and what you all think about this.....

We JUST put new plugs and wires on the truck because they needed to be changed, we did it just to replace them and get the truck running on some fresh spark, and the plugs were pretty old....didn't change the almost stalling situation....LOL....