Overheating issues

I have a 440 with a 26" aluminum radiator plus a 2L overflow expansion. It does have a fan shroud (thanks to whoever I bought that from last year on the forum) and a flex fan. Car overheats even just idling when its only 60 degrees outside. After just a few short miles it'll easily reach 200+ degrees and would continue over 220 if I allowed it.

I flushed the radiator out several times with a hose and let it run a bit just to try and get out anything that might be in the block. Refilled with coolant and distilled water. Also replaced the water pump with a high flow flowkooler and one of their thermostats. So far nothing has helped at all. A local shop let me use their block tester and assuming I used it correctly didn't shown any signs of a leak. When I flushed the radiator outside of the car, I get clean water passing through it within seconds, I really don't think the radiator is the problem but I have a radiator shop that says they'll clean it out and inspect it for about $150. I'm not sure where to go from here.