There should be a way to use a multimeter to shoot it as it is just a potienometer. If you know someone with a predator for your year truck you can check your switch that way. I have read on other forums that people have had no throttle response and had to idle to park somewhere. I don't think you would get a code unless it was completely open. One other thing that you can do is to see if the thottle move freely with your hand...if it is binding on say the carpet, then that could cause what you are seeing.
I think it is the whole pedal assembly. According to alldatadiy, it says to check it with a scan tool without starting the engine...just have the key in the run position. That way you can use your hand and not your foot. As far as the rpm going up and down....that is probably the fuel pressure regulator valve doing that.....it's called a loping idle. some trucks do it so bad that you can hear it. +- 50 isn't that bad I don't think....I will have to check mine out now.
Yes, APP is the right term for the sensor I am talking about. I checked my truck last night and it only varied about 15 rpms at idle. the FPRV is on the engine. As far as what you are feeling with the truck just acting sluggish and then taking off. Have you been changing the power levels much with the bully dog? My predator kinda does the same thing.....if you give it a little throttle, sometimes it doesn't take off fast, then it decide to pull hard. Also, when this is happening, is the truck at operating temp or is it cold? Also, I would try and clean the mass air flow sensor as it might have some dirt/oil on it from the k&n. I would just use electrical contact cleaner or rubbing alcohol and a q-tip...be very gentle with the resistors on the MAF sensor. Also, your wastegate could be going out.(blowing open) You don't have a boost guage do you?