Trans temp doesn't move from 0degreC

I'm trying to log my tranny's temperature since i will install a front mount tranny cooler on my 07 trailblazer ss e67 and i want to have a before/after comparaison... i added the Transmissions/General/Trans Fluid Temp (F) channel and went for a ride.. temperature is stuck at 0C and won't move at all.. It is suposse to work since ppl with tbss are able to log the temp with hp tuners

Anyone ever had this problem?

While playing around I found 4 (5?) different/unique PIDs that all said they were Trans Temp. At least one of them only read zero, the others were all in agreement.
Logging the 'same' parameter multiple times also played havoc with the Trans Temp gauge in the scanner and caused it to fluctuate between zero and the correct temp.