Thanks all for the help! I do pay attention to the temp gauge and there haven't been any overheating issues since I've owned the truck (about a year and 3000 miles now). It sometimes will make a small puff of blue smoke on startup if it's been sitting a few days but I wrote that off as typical old Mitsubishi. I replaced the plugs about 1500 miles ago or so as part of some routine maintenance but the ones that came out didn't strike me as bad and it had been running normally. It did have a bit of lifter noise on startup and I ran some Seafoam in the oil (in the recommended amount) for a couple hundred miles and it mostly quieted down, the recent oil change was to get that out.

I haven't seen any smoke under acceleration apart from this recent stuff. Even now it runs great apart from the idle thing but it's sidelined until I figure this out. The only recent changes I can think of that would be relevant were the Seafoam and my nephew making it buck around like a bronco while learning to drive a stick. Maybe related, maybe coincidence... who knows.