tire monitor system

Well here goes a long story, my 04 4x4 suburban had a low tire light on and a message to check tire pressure. Went to dealer had it check told me the back two pressure sensors were bad, did not have parts in stock. Recommended go next door to tire store and see if they have some. Went next store they had some aftermarket ones that were supposed to work, I bought them had them install the sensor, relearn the system and the light went out, left the tire store and did not get 3 blocks away and the light comes back on and message says check tire pressure, turn around go the the dealer he hooks up the scanner and tell me the back sensors are reading only have of the pressure that is in the tire, he manually checks the pressure and the front and back are at 36psi the scanner says the front have 255kpa and the back have 125kpa, dealer does not know what is wrong we check with tire store and they have used these sensors in other suburbans with no problem, I did notice the old sensors were blue and the new ones were red, but they said that was because they were aftermarket, any suggestions what to do next, we only have one dealer here the next one is 165 miles away.
HELP.
Thanks David

I would suspect the aftermarket sensors.
It is hard to diagnose something like that without having the vehicle in front of me.
There is a diagnostic tool just for the TPM system