99 Suburban with front and rear ac (separate controls)

I'm having a difficult AC problem for a customer of mine (I am from a shop)

Front Vent temperature (with AC thermometer): 75
Rear Temperature: 65
Compressor is definitely good as there is only one. I even changed it to make sure but... same.

Something odd is that when pressing accelerator (still parked, not moving), it gets colder by roughly 5 degrees.

I've already evacuated and recharged so there's definitely no moisture in the lines. There are no visible leaks and the lines aren't in hard places to see.

Heater Control Valve and Blend Door Actuator seem to be working fine. Valve closes all the way and actuator rotates completely without hesitation.

Any suggestions or past fixes??

 

Possible blocked or very dirty condenser core.... but I suspect there is heat leaking in from the heater core... try disconnecting the heater core from the picture and see what happens...
Also how is the front blower fan speed?

 

That was my next step. Do you know of anyway to check its internal condition without removing the condenser? It's kind of a long job but if I have to I will, I've already started removing the lines.

 

The fan speed is normal and stays on like it should. I'll take your suggestion about the heater core and get back to you. Man, I've done hours of research on this topic and I got no correct answer. It looks bad on the shop because the customers don't understand how complicated the situation is.

 

FYI,
when I say that the condenser could be blocked, I was referring to it being dirty bug gut riddled from the outside not necessarily blocked internally...
You can try placing a box fan in front of the condenser or running water over it and see if the vent temp changes but I suspect it has to do with heat being introduced by the heater core....
Do keep us posted