Be fore you go buying a rad, is your shroud complete and installed? Including the little side pieces at the side of the radiator covering the gap to the rad support. You want as much air as possible to go thru, not around, the radiator and fan.
A stock 4.3 should be able to sit quite a while in hot weather w/o overheating with all the stock components working. 1000's of them do every day in CA, FL, and AZ w/o problems.
On the s10/ Sonoma / Blazer/Jimmy 4.3l if you don't make sure the bottom of the shroud is locked in that fan will eat it. I just had that happen on my blazer didn't make 100% sure it was locked in right and the fan tore the bottom of that shroud into pieces. So that's why I changed over to electric fan today.But that's not what the cool kids want.