1986 GMC C3500 Converted GMG 1-Ton to 400 ci gasoline

I've converted my 1-Ton diesel to gasoline. I am having a problem getting the engine to cool down to a good operating temp. Even though I have a 160 degree thermostat, it still runs at 200 plus. I have put in a heavy duty aluminum radiator and I run the oil and transmission cooling units out front of the condenser as separate units.
What can I do to make this engine cool down?
Dale Pollard
Milton, Florida