2002 Dodge Ram 1500 4 door remote lock/unlock problem

On my 2002 Ram 1500 4 door king cab truck:
I have an aftermarket keyless remote start/alarm/lock/unlock system.
It has always worked ok, but lately when I use the key fob to turn on the alarm to lock the truck, (doors lock and alarm is armed OK) when I try to unlock it with the key fob it disables the alarm but doesn't unlock any of the doors, even if I press the unlock button multiple times. I have to use my door key to unlock the driver's or front passenger door then use the normal electric unlock button inside the cab.
Any ideas?
Thanks in advance.

Do you have electric door locks? Do they lock & unlock the doors with equal force?
How about operating the locks manually? Do they pull up as easily as they push down?
Jes' thinking about stiff linkages.

Do you have electric door locks? Do they lock & unlock the doors with equal force?
How about operating the locks manually? Do they pull up as easily as they push down?
Jes' thinking about stiff linkages.

Thanks for the reply.
The Door locks are electric.
They all lock and unlock with equal force.
They push up and down with equal force.
The Linkages seem to be fine.
The remote command to lock works fine.
The remote command to unlock is what sometimes/most of the time doesn't work.

I guess would be your aftermarket remote "brain" is going out. Unless you have a good warranty on it, it's probably gonna die in the near future. Or change out your remote battery and see if it changes.