1994 Chevrolet Suburban Chevy That Recently Purchased 5 7l 350 Engine

It has been overheating at about 255 according to the gauge and the "check gauges" light comes on. So far....I've replaced the thermostate, very slight improvement. Next it was the radiator. Improved to about 230 degrees. Next, found out the wrong fan blade was in the truck. Put the correct one in, slightly better at 220 degrees. I have now replaced both sensors to the gauge and computer. Now when I start the truck from cold, the gauge goes right to 260 with a couple of minutes and the "check gauges" light comes on. I am completely lost at this point. By the way, when all the other items where being replaced, we had a temerature gun on the thermostate, side sensor to gauge, top and bottom radiator hoses and all gave results ove around 160 degrees. Any further help would be greatly appreciated.
Currently unemployed and need vehical to go on interviews and cold calling.
Stumped