no rear heat

I have a 95 burb 4x4 1/2 ton with no heat in the rear. The a/c works good both front and rear, but the heat only works in the front. It doesn't matter if I use the front or rear control. All suggestion are welcome!:confused: :banghead: :banghead:

Does anybody rear this forum?:banghead:

Could be a plugged rear heater core. Could be a rear temp control door problem. Are both heater lines to the rear warm or hot to the touch? Has there been any recent cooling system work done? If yes then it could be just air in the system which takes some time to work its way out.