odd door lock issue 05 silverado

I just purchased an '05 Silverado.  I used to install remote starters, but have been out-of-it for about three years.  This truck has a AutoPage RS-900 starter, and a DEI 1700G passlock bypass/door lock module in it as purchased.

The problem I have is when unlocking the truck with either the remote, or even using the factory door unlock button, the rear doors do not unlock.  Both of the front doors work as expected, with both the remote and door button, along with when you put the vehicle in drive/park, etc.

I checked all of the door lock wiring, from the 1700G, to the RS900, etc., and all seems to be fine.  I also looked at all of the programming options in the owner's manual for the truck, and both of the units listed above to see if you could program this anomaly to occur.  I also checked the two wires from the BCM that regulate unlocking the rear doors, from the purple connector, and they are intact (at least to the kick panel).

Does anyone know of any programming option that would disable the rear door unlock function with this vehicle's BCM, or with either of these aftermarket units?

If anyone has any suggestions, it would be appreciated.  Thanks.

Thank you two for the replies.

I had the left side door panel off, and all seems normal in the door.  I checked here first, before getting out the multimeter though.  I guess since there are no programming options, that will be the next step.

I just found it odd that the back doors don't have a problem locking with the switch or when the truck is put into gear, but never will they unlock.  It ticks me off sometimes, especially since the system has been changed quite a bit by an aftermarket alarm/remote start/keyless entry system... you'd think it should work better than factory!

Thanks again.  I will post back someday when I find the problem.