the sensor is located inside the cover assembly on the transmission control valve. It is at the end of the control valve and has the harness made onto it.

and yes i was going to suggest replacing that display so you can see whats going on, its pretty important to be able to see things there :o) The only other way to access the system that i know of is with laptop diagnostic program from hyster. Purchasing a service and parts manual would be a good idea in your situation. They will not sell you the diagnostic program, that is a certified dealer tech only item not available to the public.
You can diagnose most of what is going on with this truck through the dash display so get that taken care of first.

as for finding out information on your machine, your dealer can give you that over the phone when given a full model and serial number. The engine type and other information should be on a dataplate on the engine.
The transmission should have it's own dataplate with information on it.