Well, first thing in the morning (before) it wouldn't lock up until a minute or two at 45+ mph. But after that it was usually 42-43 at normal accel to lockup. Drove it last night after messing with it and it was locking up at 47 consistently. Took a long sweeping left turn at 25 or so (nothing crazy) and didn't lock up after that turn, and I was doing 50-52. This morning, go out for a ride, locks up at 47 again. Just a little while ago, went for about a half hour drive to run errands, and stops locking half way home. Stopped somewhere for about half hour, starts locking at 47 again when I leave. So I'm thinking if I had a wiring harness issue, it'd be there and not go away regardless. Leaning more toward the actual sensor now, maybe heat is getting to it?

 

Open your hood and see how many relays are on the drivers side fender just below the hood spring. If you have 4 the rear most one is the PTU (part throttle unlock solenoid). If it is there you might want to check that.

 

I do have 4 relays, and they all look original. The rearward one has 2 plugs going to it, one of which is just a single wire. Is there a particular way to test it? I know I'll have to dig up my multi-meter and go from there.

 

Most relays have a wiring diagram on them, if not you are going to have to figure it out yourself. I know that may sound bad but I have researched this PTU system and have been unable to find anything on it and I have not personally seen a truck with this system on it. I know it exists because my truck says it has a problem with the PTU, by showing a trouble code 37. That is why I did as much research as I have and found out the system is not on my truck. I can't even find a wiring diagram that shows the PTU system although I did find a picture that shows its location. If you can show a picture of the relay prongs with the numbers on it I might be able to help you figure it out. Sorry I can't be of more help.