Tps sensor??? Where is it an how do I get to it

So I have a 1994 GMC Crew cab 1 ton 4 wheel drive dually with a 6.5 l turbo diesel and I have been having shifting issues... First gear wants to tach out, then if you let off the gas pedal a little bit it will shift into second and then in second it kind of goes limp into third and you just lose a lot of power online I read in a different forum I believe that the TPMS sensor will cause erratic shifting and loss of power like I'm having. I bought the new sensor and I cannot for the life of me find where it goes and I am new to diesels especially the 6.5 I spent various hours trying to find the location on the internet and on YouTube with no luck... If someone can point me in the right direction or tell me what they think is my problem that would be greatly appreciated I really want to get this truck back on the road but I'm not having the best luck

Welcome aboard!

The throttle pedal IS the TPS. (TPMS is Tire Pressure Monitoring System). The APP module (Accelerator Pedal Position) is the thing the skinny pedal moves when you step on it. If you bought a TPS, it's for a previous model with MFI (mechanical fuel injection). The APP is the only physical input to the system. If it has issues, the "Service Throttle Soon" lamp will be on. It's triple redundant, and will whine at the first glitch. Shifting issues can be related to poor grounds, connections, the ign. switch, or any number of electrical issues. There will often be DTC's (trouble codes), and the SES lamp will be on. Fortunately, being a 1994 model, you can read the codes with a paper clip. If no codes, look for supply power issues, such as the ignition switch, which can cause weak or intermittent power.

How's the fluid level?