overheating problem with 1993 jimmy

have you tried, the water pump ,

i agree with chevy, the water pump maybe froze up and not working properly, the bearing may be gone, easy way to check this is to to look for leaks around the pump itself, take off belt to pump, and try to wiggle the fan blade up and down, it should be solid, if it moves, then the bearing is gone in the pump, not a hard fix, if you know what you are doing, this should take no longer than an hour to replace, make sure you have all the areas dry before re-installing the pump, you will have to dry out the holes to the block with a rag so that the sealant can cure