I already replaced both the Input AND the Output speed sensors on the transmission, but I'm still getting the intermittent code P0720 and the code for limited power. Basically, my PCM is putting the truck in limp mode because it's not sitting accurate or consistent data about how fast I'm going.

I went and bought the PCM probes for my multi meter, but I'm stuck..no clue how to proceed from here. Please help

 

I believe, not sure, the PCM looks at three different speed sensors and if they do not agree to the expected parameters you can get limp mode
Two are on the left side of the trans
1) OSS or output shaft speed sensor
2) TSS turbine shat speed sensor
and one is located on the rear differential. I would pull and inspect the one on the rear axle and make sure its not full of crud like iron filings. Might help.

 

These are the codes I got when my dash said "TRANS FAULT” and it went into Limp Mode.

 

Is there a diagram somewhere that will show me the speed sensor pins in the PCM socket and which, of the three sockets, I should be testing on?

 

helps to Identify what you are working on

 

I would focus on the throttle body problem first

Here are diagrams for 05
http://WIRING DIAGRAMS - DeVoll http...searchable.PDF
Since you don't say what year your working on, there may be some differences, but the vast majority of things will match up.