Thanks for the info/advice! So far I’ve replaced the radiator, water pump, thermostat (2x), timing belt, radiator cap, multiple flushes and refills of coolant, etc. At this point the problem is that the engine gets so hot after turning it off (if I’ve been driving at highway speeds for at least 30min), that I can’t drive it again till it cools off, which can take a long time. If I fire it back up within a few minutes of stopping (for instance, after getting gas), even if I let it cool off to normal temps, it’ll slowly start heating up after a few miles. Once it reaches about halfway up the gauge, it gets hot exponentially faster.
Still sound like a pressure issue? Or perhaps wrong mix/type of coolant? At this point I’m at my wit’s end and multiple mechanics have scratched their heads without a clue about it.