Overheating my car is fine it seems when its idoling but when i start to drive it it starts to over heat recently i forgot to check the oi level the oil light went on and then the over heating occured i parked it over nght to let it cool down and stll it over heats could this just be a thermostat problem? or sumthing much bigger

If you are loosing coolant and cant find any leaks check your oil level. If oil level is rising.you have blown a head gasket or cracked a head. Common when an engine over heats badly.

Check the transmission fluid level. Also check the rear differential if your car has one ( I think the 99's were still rear wheel drive) for fluid. If either of these are low, the fact that things are fine indicates that the low fluid level is causing problems. Also, the trans fluid should be a nice pink color. If it isn't then the transmission is not in good shape and should be looked at again by the rebuilder. If the fluid levels are fine, have the rebuilder check the trans again to see if he missed something.

The issue with the temp gauge is entirely separate except if you mean that the car begins to heat up when the shifting problems are occurring. If the temp gauge goes way up then comes down quickly regardless of how the car is being driven, the thermostat may be sticking and should be replaced. If the car is hard to drive and then starts overheating, the transmission may well be defective and causing the engine to work harder than it should.

check throttle position sensor,check cables for sticking

Have you checked your coolant levels as well as thermostat and waterpump functions? These can all atribute to engine overheating.

Check the cooling fan motor and of course the fluid level. If the temp is changing thru the heater it could just be low on coolant , leaking from ? Two wheel drive have an elecrtic cooling fan only, make sure its spinning up when temp is 3/4. If not its probably the fan motor. Can be checked with a test light .

It sounds like water pump may be your problem. It circulates a 50/50 mixture of glycol (or some form of) and water through the engine block and cylinder head and back through the radiator. In the radiator the mixture is cooled when air passes over the fins of the radiator. This is accomplished by driving or a mechanical/electrical fan when stationary. The water pump also circulates the mixture through the heater core giving the car heat. If the water pump is not circulating the water back to the radiator to cool, it will overheat. More heat is caused by the engine when driving (much less heat when idling), hence the overheating while driving.
I hope this helps and good luck!

3.1 AND 3.8 ARE KNOWN FOR UPPER AND LOWER INTAKE GASKETS

hello, have you ran a scan tool on it yet to see if its not your coolant temp sensor or other temp sensor if you don't own one you can have any place like auto zone run one for you for free you'll have more of a idea of whats wrong even if your cooling fan is at fault it'll let you know. when your chevy is at idol if the cooling fan is'nt kicking on then that's a good starting point,also check to make sure your anti freeze is'nt low and easy but over looked problem and your anti freeze cap could be bad and wont force the right amount to pressure through the cooling system also make sure you dont have air in your system when you changed the thermostat did you bleed the system through the bleeder valve mounted on the coolint system.and make sure your drive belt has proper tension even though you replaced the pump the drive belt has to be in good condition it drives the pump.also check your cooling fan fuse and the relay for it.

Replace the thermostat. If thermo is stuck open, coolant only heats up when there is no flow over radiator(idle) and then cools down when driving. Also, check coolant level, same response as stuck thermo.

check the coolant level on the radiator