Haven't seen you here in a bit. Good to know you're still kicking around.
Try these, in this order. One at a time. Except the last one.
What thermostat did you use? I'd suggest the low-temp unit. It's MotoRad part #439-180
. It will give you some headroom at idle with poor airflow, like sitting stopped on hot asphalt on a bad day, or under a heavier load. It just gives you an extra few degrees of temp climb before getting to boil over. I have read that they flow a little better but I don't know if that's true. Some sort of internal spring loaded bypass. Not sure on that.
All radiators are not alike. If you bought a cheap one, or just ended up with one and over-paid, It won't perform like a good one. The Nissens is a very good replacement and under $200. The others are all pretty much Chinese. maybe you have a local radiator shop that can flow test it. I've seen under the tanks on some of those cheap imports and it looks like they have monkeys soldering the cores to the ends. No wonder they don't flow.
You might try a water pump replacement. Use only a premium aftermarket with the metal impeller. Delco Pro is $65 on Rockauto. Impellers can deteriorate due to the effects of cavitation and will eventually reduce coolant flow.
If you're still getting warm, an auxiliary oil cooler will definitely help. Right now, the system is relying on conduction internally to cool the oil. This places a load on the primary cooling system. Running the oil through a separate system relieves a big burden from the radiator, freeing it up to carry more load.
Also, check your aux electric fan. They are a high failure rate item. It should kick on at startup for a moment and any time the AC is switched to max.