Continental overheats

My neighbor bought a 1996 Lincoln Continental that overheats after about 3 hrs of driving. He says he changed the thermostat, radiator, all hoses, water pump and cooling fan. And it still has problem. Can anyone think of any thing else that can be checked to resolve this problem? Thanks so much.

Three hours of driving? 3 hrs puts you pretty far down the highway....

What kind of driving (city, hwy, mtn)? What climate (city, state)?
Does it overheat when idling, not driving?

Is it actually overheating, or is the gauge just reading wrong?
Hows the coolant level holding up? Having to add coolant constantly?
Was the air burped from the system when coolant re-filled? (see other threads)
Was the overflow pressure cap tested to be good?

Any constant bubbles in the coolant recovery bottle?

If he changed the thermostat and all else is fine, is the return hose "hard" after driving? Any blue smoke out of the tail pipe? Hope it's not the head gasket going? Cross your fingers!