2001 Chevy Blazer Truck Doesnt want to go in the mornings

Ok I have a 2001 Blazer 4 door. My truck ran fine about 3 months ago. I had to have the Clutch fan replaced 3 months ago Cause before when I ran the A/c the truck would over heat after 30 mins or so an didnt want to accelerate like the transmission got to hot or something, But as long as I didn't use a/c it ran fine and shifted fine. Now that I have replaced the clutch fan everytime I get in my truck especially in the am it does the same thing I have to warm the truck for at least 15 mins before I go anywhere. Its like my truck doesn't want to go an its very sluggish an sounds like my rpms are really high, but after 6 mins of driving it finally git going an runs just fine, also it does it if I run a/c on high for long periods of time. But if I keep it on low I can run it for long periods of time. Can you please direct me as to what could be causing this?
P.S. I had the clutch fan replaced as well as the thermostat