ok i replaced my clutch and my slave cylinder in my 93 ford ranger. and everything was going great. i started it early this morning. turned the heater on and the defroster. got in and it was really warm. doing great. drove it about 4 miles andthe heater started to push out really cool air and my truck started to over heat. i replaced the theromastat on it about 7 months or so ago. could it have already gone out??
or do you think it could be something else??

 

It's rare to have those two conditions at the same time. If the thermostat is stuck open it shouldn't overheat. If it is stuck closed , it will overheat, but not blow cold air,,,,,,
unless you are out of coolant. Did you check the coolant level?

 

coolant seems to be fine. but i topped it off and it run a little better but is still dont have a heater and it still gets really warm.

 

your heater core lines might be clogged

 

Its beginning to sound like you have more than just a possible plugged heater core. Do both hoses to the heater get hot? If so, chances are the core is at least open, but still could need flushing out. The overheating could be related to the same problem, cooling system may need to be flushed out. If you can see the inside of the radiator, does it have a lot of white corrosion around the cooling tubes? If so , it wouldn't hurt to have it boiled out by a radiator shop. Only thing , when they boil out a border line radiator, you may wind up having to replace it because the corrosion has gone too far and after they remove the corrosion and pressure test , it looks like a shower head.
Let us know what you decide to do.