Overheating

look under the oil fill cap and see what color the exhaust is tell us what you see , you can do a compression test that will tell you if the head gasket is done for , common problem , A good mechanic told me that once the oil and coolant mix and get into the entire motor doing just the gasket ain't good enough because you'll never get all the crap out of it ,, the whole motor should be torn down , of course it's done all the time . If it's the 3.8 the intake plenum gaskets might be bad and causing the mix and the over heating could be a separate issue , thermostat , radiator , but it would probably leak coolant also , those gaskets should be replaced about every 70-80 k just saying

If its intake or head gaskets the parts are cheap, its the labour that sky high. If under the oil fill cap has chocolate mike sludge and you can see down to the top of head either by pulling a valve cover or in oil fill tube you see it, see if it looks like a sludge or just a thin film, either is bad if driven like this more than a few days but they act a little different the sludge will cake to the internals and try its hardest to stay in the motor resisting to be removed, the thin mix will come out with 3-4 oil changes back to back, one after another, not days or weeks a part. The radiator along with engine and entire cooling system including heater core will need to be flushed a few times or until it stays clean, this is all done after the repair. I doubt the head or heads are cracked, more likely a gasket, which hard to say but intake is likely but a compression test will confirm if head gasket is gone, not a bad idea to replace both side and do them anyway if intake gasket was the issue. This stuff in the radiator could be trans fluid mixing with coolant on automatic trans. The trans cooler is inside the radiator.