TPMS relearn mode

[sierrastrong]

I have a 2007 SIerra.  The TPMS sign in on as well as the yellow tire light.  I can't get it to go into the relearn mode weather by putting on the park brake, key on and holding down trip set stem, also turning on/off the light switch 4 times or the lock/unlock button on the key fob.  The GM dealership verified my tire sensors are all active and working. They tried a new ECM as well with no change.  Basically the GM mechanics couldn't figure out how to fix it and returned my truck to me unchanged.  Has anyone else had this problem and if so what was your solution.