terry,
since cat had so many different upgrades on the configurations on these trucks a full model and serial number might be more helpful so we can make a more definitive determination of what is on this truck.

As a general diagnosis though what edward said is one of the first things to look for when this problem occurs. A binding throttle plate in the throttle body can cause high idle problems and these systems are notorious for gumming up causing all sorts of issues.
You can remove the mixer cover and diaphragm and clean that, then squirt some cleaner down the mixer body throat and clean that out as well.
Then when you go to start the engine, it may not want to start so just keep trying till it gets running and hold the throttle wide open till it catches up and all cylinders clear up and it starts running as it should, then let it go back to idle and see if that helped.
If not then i would look at a binding mechanical issue inside the TB.
Like edward said, if the accelerator sensor is out of adjustment the engine will not accelerate at all until that is calibrated correctly and the adjustment is set correctly.

if none of this works then we'll just have to dig deeper which will mean the full 'corrrect' model and serial number of the truck.

when you say "TP sensor" are you referring to the foot pedal postion sensor or the throttle body?
my w.a.g. (and I have looked at a few of these over the years) is a bad (stuck) throttle body or bad computer. this truck should ONLY idle if the foot pedal position sensor is out of whack. you may have a bunch of crud built up inside the throttle body.
are the 2 vac lines on in the correct places(the bottom one goes to the little computer box and the top one to the distributor) do you have the lines to the fuel trim valve correct? one that looks like a tee, is not a tee)