After asking many questions and getting very mixed answers I finally found what was causing the transmission to al of a sudden start running 30degrees warmer....

My story was, The transmission had always run right at 150degrees (Sensor in deep pan) for the past year since the rebuild. My truck only has 60k on it but went billet, vb, etc... Anyways cruising down the freeway one day and my gauge starts reading 180 all of a sudden... Spent the past couple weeks asking questions and probing around the truck and turns out 3rd Gen 48RE's have a thermostat that bypasses the transmission fluid to air cooler up by the radiator. It's built right into the top of the cooler itself. I'll attach a couple pics. Anyways they tend to stick if they get a build-up of debris on them. I simply cleaned it and put it back in (only got a couple dark smears of dirt off the valve) and works like a charm again... Rock solid at 150degrees now...


So what I did, remove the bolts for the AC condensor, tied it up out of the way, pulled the intercooler, took loose the transmission cooler (did not disconnect it). You then need to remove the internal c-clip that is in the end of the bypass, once you do that I took a simple blow torch and gently heated the aluminum block around the plug and the spring pressure poped the plug right out... Remove the thermostat and spring, cleaned them all up with brake cleaner (was ok to pull out the little shaft from the thermostat to clean it, found a good bit of dirt inside there, actually used the tube on the brake cleaner can and blew out the inside of the thermostat) Then oiled it back up with tranny fluid and slid it back together, held the plug in with a phillips screwdriver and reinstalled the c-clip. Put the rest back (intercooler, AC condensor) and that was it, took maybe 45min...

Hope this helps others out there trying to figure out why your tranny runs soo warm...