I have one of those DVD's somewhere too!!! lol!!!
If everything checks out with the wiring I would replace the TPS, they are less than $100 and it comes with the complete pedal assembly. This was a very common problem with the 99-03 Superduties and if this shop was worth a Flip they would have known this!! Unless they don't use a TPS on the down under trucks?
The 1211 code is totally normal for a chipped truck. Basically your injectors are calling for more Oil Pressure than what the stock pump can provide. Nothing is really wrong and the only cure is Big Oil which also means Big $$$
NCH