If I rev the engine to 2000 rpm the temp comes back down.
Rule of thumb--which is not true in all cases--is that overheating at low speed is lack of airflow, overheating at high speed is lack of coolant flow.
As already said--look for debris in the airflow path including folded-over fins on the radiator and condenser.
There's two dozen other potential causes of overheating, including but not limited to lack of spark advance, lean air/fuel ratio, missing cooling-air ductwork--fan shrouds, air dams, etc., dragging brakes that make the engine work harder, water-jacket blockages, and so forth.
Temp gauge is bumping 225, not sure how much I trust it
Worth verifying the temp gauge with a thermometer in the radiator, an infra-red temp gun, or a second temp gauge and sending unit.
An infra-red temp gun can also find cold-spots (plugged coolant tubes) on the radiator, if the plugging is bad enough, and if the condenser isn't in the way.
I think my radiator might be fouled and the sludge hardened up while sitting for a month while rebuilding the engine. Next step is a coolant flush. Any thoughts?
How old is that radiator? If it's original, it's likely overdue for replacement based on age and miles. If you have a local radiator shop, you could ask them to clean it, and see what happens. Radiator shops are getting scarce--the Communist Chinese along with the EPA are running them out of business. One offers low-dollar "new" replacements, and the other cries and whines about the waste they generate.