My 96 MKVIII LSC is overheating. on 1996 Lincoln Mark VIII

I filled coolent via the filler tube on manifold & burped as instructed.I changed the heater core (not an easy job),water pump,thermostat(about 1yr ago), oil filter adapter and all parts with OEM parts except the thermo. Belts are good. No water in the oil or vice versa. No noticable leaks on driveway. Any suggestions ?

Asked by for the 1996 Lincoln Mark VIII
possible issue with exhaust system. cat. conv. could be clogged.
Not the cats, they were replaced 20k ago. have free flow exhaust at the tail pipes and level as well as stopped on a hill. The car would certainly stop or chug going uphill, and we have a lot of hills to get to our house. Has a lot of power. Thanks anyway.