Goddard, I never ran a temp. gauge for the transmission, can't offer much advice there. Guess you could always remove one of the PTO covers during your next service and tap same for a probe ? Sure that someone else has a simpler solution. One is the Fast coolers, which are already set up for a temp. probe if you don't mind spending the bucks for the covers.
Engine oil temp. is a piece of cake. On top of your oil filter housing you will see a 1/8" NPT silver plug. Remove that plug and screw in your sender for engine oil temps. , works like a champ.
Scott W.