When I lived out in Pa. I had wrecked my then-new car and needed a bang-around. I found a `75 Dart (this was in `94) that had only 32K on it. Nice clean 4 dr. 6 cyl, A/C, automatic Brown & tan. The original owner, she said "it's never been out of Lancaster County. Never run on the highway". First time I attempted to drive back to NY with it to visit family I had the SAME EXACT CONDITION and eventually replaced exactly the same parts, PLUS I reverse-flushed the cooling system. Still overheated. At that point I wrote it off as sediment in the block from the car sitting that was fused in there…. and it wasn't until recently that I ran across the same condition in a late model Infiniti when I was still doing that. Here's what I learned.

When I reached-out to the factory service hotline for repair incidents similar, and what the resolution was, I was told that once a block is scaled-up around the cylinders it will never transfer heat correctly back into the water jackets. I had to replace the short block in the FX-35 to fix the overheat problem. We threw a whole bunch of parts at it too going from diagnosis to guessing. Is this a vehicle you've owned for a while? Or is it a recent addition to the garage? Granted, the Infiniti was aluminum, but it sounds like your gakked-up around the cylinders…..