overheating

I have a C4 94 Vette that over heats . We have flushed the radiator, put in new thermastat and coolent . The fan runs and we even put slick50 in the oil when we changed it( was supposed to lower temp 20 degrees) , but it still over heats when sitting still and when running the air.  Need help!!  

Items you haven't mentioned:
1. Radiator cap..16-lb pressure. Cheap and easy access for replacement. Make sure engine is cool when replacing it.
2. Radiator hoses..inspect to make sure the inlet hose is not collapsing, no leaks on both the inlet and outlet hoses.
3. Is your temperature sending unit working properly? You might not be overheating at all. Have it checked...
4. Water pump. Is it working properly? Are you the original owner? If not, verify original owner did not install an "underdrive" pulley. Have a trusted mechanic to check that the pump is up to snuff. Note: keyword is "trusted". Others are known to replace parts that do not need replacing. Just watch who you deal with...  

What temperatures are you seeing? Are you using the analog & digital temp readings?  

I would check for a blown head gasket. water pump only pumps water. exhaust gases in coolant will stop coolant flow. I hope I'm wrong, it only takes 1 overheating event to warp an alum. head. good luck  

Has same problem with my 92 coupe.  Discovered that temperature guage was was giving a false reading approximately 20 - 25 degrees hotter.  

Same problem 94c4 I change the radiator for a "HEAT BUSTER" 3" thick now no more problems, it icrease almost to double the capacity of coolant. I was tired to my car go over heat little expensive but it works perfectly in long lines of cars w/ac on, I expend  $300 bucks