95 blazer water pump replacement?

Truck (1996 s-10 blazer 4WD, 157K) has been running hot lately and I want to replace the thermostat and waterpump (I bought the truck with 90K and have not changed the thermostat or water pump) before winter comes. I guess I should also change the radiator cap as well. I have been told that waterpump replacement is a pain, that you have to take off the intake? Does anyone have any tips for me as I would like to do it myself.
Also, another strange thing has been happening with the AC on....if I get on the throttle a bit hard, the AC switches from coming out the front vents to coming out through the defrost vents....very strange. Any suggestions on this would be much appreciated as well.

Thanks in Advance,
Greg

Water pump replacement is like a small block chevy. You do not need to remove the intake manifold ( I love hearing these automotive urban ledgens :iceslolan )

Your A/C vents are vacum controlled, check your vacum lines for leaks (In the engine compartment).

Thanks GMMerlin. I tore it down last night and didn't seem very difficult. Glad I didn't take the repair shop up on their deal to it!
Only thing I am having trouble finding are the block drain plugs. It was getting a little dark, will check again this weekend.
Also, thanks for the tip on the AC vents, I will go over the vacuum lines.