Overheating Problem HELP

I have a 94 Caprice with a 5.7 L. The other day the damm thang started overheating on me while i have tha AC on well anyways i changed the thermostat and it worked for about an hour and then started doing the same thang last night after driving it around about an hour.When i lifted the hood up i noticed that the exaughts manafold was red on the passenger side and when inside i smelt like something burnig from that side when inside the vechile. Ive changed the spark plugs,wires and 02 sensors put when i changed the 02 sensors the passenger side it was black pithch black.Can somebody help me i tired of waisting money on parts that i dont need.
Thanks:banghead:

have you upgraded the radiator to one that is capable of dealing with a 5.7 litre engine and the heat it produces?
have you checked that there are no air bubbles in the cooling lines?
do you have the correct thermostat for that engine, and not a "hotter" or "cooler" one thinking that it will make you faster?