I don't know the answer to your question, but might be able to point you in a direction to go. A trans. temp. gauge is standard in a GM pickup with the Allison Trans. Go to a GM dealership and ask them. Bet a mechanic could show you.
I like them installed in the pan because this is the temp of the oil as it is pumped into the working parts of the trans. Some install in the cooler line. Most any major parts will have them and performance stores will also sell them with directions. Go with what GTS said and ck with chevy dealer.
Been second thinking myself and thinking now that it might be better to have the sender in the line out of the trans going to the cooler. That way you would know the temp of the oil after going through the guts of the trans. Hmm be great to have two gauges. One in the pan and the other in the out line. Bet it would show a slipping trans.
Having the gauge in the "to cooler" line will show the hottest point in the system. It's that temperature that is the best indicator of transmission fluid life. Many of the electronically controlled transmissions of today have a sump (in the pan) temperature sensor. That sensor is intended as an input to the control system, and as a diagnostic indicator of the temperature of the transmission itself. However, to monitor the temperature the fluid is really exposed to, the "to cooler" point is still the best.
If at the "to cooler" port the fluid sees 300 deg F, but you're monitoring a sump temperature of 250 deg F, you'll never really know the fluid is breaking down.
You have my interest - I never knew the temp of the fluid increased with age. I just had the fluid changed in my coach, and the temp runs between 175-200 on the digital guage. What temp should I look for that would indicate a fluid change and/or problem?
I was not very clear. The temperature of the fluid does not increase with age. What I mean is the hotter the fluid runs, the shorter the fluid's life. Fluid run at 300 deg F will oxidize and break down way before fluid that runs at 200 deg F. Running 175 - 200 in the to cooler line is very good. Fluid change intervals should be as per the transmission manufacturer's recommendations.
300 deg F is a point at which Dexron fluid breaks down very quickly. It's a temperature it can only stand intermittently. On the Allison retarder models, they are allowed 330 deg F intermittently, but only because it's a retarder and they normally have a huge tube and shell water/oil cooler in the system to cool the oil back down very quickly.