probably need new head gasket
check you water (coolant) level, make sure thermostat is working, radiator leaks, sensor problem
have the engine timing checked. if the timing is wrong the engine will overheat, are you loosing coolant?is the fan working, is the water pump working?
when overheating occurs at highway speeds the cause is usually. a radiator or coolant circulation problem, Check for a restricted or clogged radiator.
check your fluids it is probably low on antifreeze and if it still does it change your thermostat that should fix the problem
check thermostat and/or water pump
did you replace radiator hoses i have seen hoses collapse and cause overheating while driving and radiator could be clogged. also did you bleed your cooling system according to owners manual
You may have the problem of your intake manifold gaskets. They are a problems on the lumina. I had to have mine replaced due to the same thing. Also check if your coolant is mixing with your oil if it is. Than it is definitally your intake manifold gasket.
You need to take it to a qualified mechanic for repair or you could runin the engine - have you looked to see if there is a leak in the cooling system?
Possibilities: Cooling fan not working. Low on coolant. Clogged radiator, radiator hose or block.
have you checked the fan
head gaskets they all do it i have two 99 sts with the same problem cost about 2500 to fix correctly.
you should have your cooling fan checked or temp sensor or relay or check your coolant it might be low or thermostat might be no good it should be one of these