Caterpillar CX28 coupled with CAT C9 engine...gear shifting issue

Hello all I am Bill Townsend from London,UK. I have CX28 Caterpillar transmission and it wont shift from 1st gear. It is only shifting in 1st and reverse gear and neutral. It will not shift to 2nd 3rd and so on. Please suggest what possible problems can be stopping the transmission to shift. I did a little bit research and found the following aspects that might be effecting it;

1- Oil cooling system not complete? (note: the cooling system that is the heat exchanger and auxiliary fans are disconnected and bypassed)
2- How does the cooling system switch the auxiliary fans to operate and what controls it?
3- Lockup clutch not engaging? (What possible things that can inhibit the ecu to not engage the lockup clutch)
4- accelerator pedal WM526 not calibrated? (How to calibrate and make sure it is rightly calibrated)
5- Engine RPM?
6- Transmission Oil pressure?
7- Transmission Oil filter blockage?

Please suggest more and please suggest actions how to check for the above mentioned issues.

Caterpillar CX28 coupled with CAT C9 engine...gear shifting issue