Heater question

Here is one that is absolutely baffling me...I replaced my heater core in my 95 aurora about a year ago...worked great, but this winter I have the darndest thing...when I run the heat, no matter what the temp I put the control on, I get average mid temp out of the middle and drivers vent...the passenger side blows nice and hot. I checked the actuators and they seem fine...replaced the HVAC control, still the same thing...any suggestions?

I also have the same problem but have not done any work to my heater core. Problem was noticed this winter, nice and hot on passenger side but warm on drivers side! I will watch this thread for replies.