This will be a bit of a long post but by posting all the symptoms and steps already taken, I'm hoping to get to the bottom of it. This is regarding a 2001 Yukon, SLT 4WD.

Only after my truck's been running for an hour or more, the amount of air being forced through any of the cabin outlets diminishes. The fan speed doesn't change, only the amount of air coming out of the vents.

I believe we've already replaced the actuator, but the problem still persists. One other thing I noted this weekend: If I've got the fan speed on 4 or 5 and move the thermostat from hot to cold (or vice versa), the temperature "sticks". If I lower the fan speed, the temperature will change to the new setting.

I have manual controls (no digital).

Any ideas on what this could be? The dealer won't do anything to it unless there's a code displayed. I've even taken it to them when the problem's happening and they can't/won't do anything because there's no code.

One other thing I noted since we replaced the compressor this summer: there's a TON of condensate that drains from the unit everytime I park it, no matter whether it's been on heat or AC.

Any help is greatly appreciated.

HMMM..its not hot where you are is it?..the a/c freezing up?..
have the cabin filters been checked/cleaned?
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there are 4 actuators...left/right temps,mode and recirc...

i'd start with the filters though

Well, it's 41 today but it was 78 2 days ago.
It doesn't matter if it's when the AC compressor's on or off. If I'm blowing AC air it stops coming in the cab at full fan speed after an hour of driving. If I'm blowing the heater it stops coming in the cab at full speed after an hour of driving.

Doesn't matter if it's on recirc or not either.

Filters are all new.