If you have a stand alone engine ECU that offer extra channels you can setup sensors to datalog your transmission.
This is something that requires minimal work. There is already a sensor in the transmission for this. You use the upper transfer gear pulse generator.
This is just like the input shaft speed. There is already a sensor in the transmission for it and you use the lower end clutch pulse generator.
On the front of the transmission case just above the pan flange there is a sensor sticking out. This is a transmission temperature sensor.
This is a section from the ATSG manual from the Downloads Page. This is all of the ports for checking pressures on all of the circuits. It also tells you the pressure tolerances. Im sure you can setup pressure sensors on each of these ports if you have the available inputs on your ECU or if you have a Racepak datalogger. There are also pressure/temp sensors such as a Bosch PST-F1 where you can read both pressure and temperature at these points if you wanted. This is one of those cases where a picture is worth a thousand words so i will let the illustration do the talking. The thread of these ports is M8 x 1.0. a pressure tested that will work for these is the Cornwell GSI3150.