What water pump are you using?
I had a brand new one from NAPA that wouldn't keep my big block under 210* in 80* ambient. I spent too much time and money trying an aluminum radiator, added extra coolant steam lines to the intake manifold, different thermostats, because everyone said that a new unit shouldn't be the problem.
I ran it that way until winter came and I noticed that I didn't have much heat in the cab.
So I spent the money for an Edelbrock water pump rather than gambling on another parts store unit. This completely cured my problem. I had more hest in the cab with a 160* T-stat, than with a 195* and the NAPA pump.
I went back to a 180* in it and closed the valves on the steam lines.
My point is, check for decent water movement somehow.
My '90 Jimmy is using a 4 row copper/brass radiator, new autozone water pump, a TBI fan clutch with an 11 blade Vortec plastic fan. It's a serpentine accessory drive. I use my A/C while wheeling on the rocks of Moab in 98* heat, in a black truck.
It's a 350 with aluminum heads and EFI.
So an Edelbrock pump isn't mandatory.
I do use Flow-cooler thermostats.