95 Tahoe Running Hot

[PAMUSTANGMAN]

I have a 95 Tahoe with the 5.7L and 182500 on the clock. I had a leak at the intake gasket pushing coolant out the left front corner and running down the head. I did the intake gasket and put in a brand new 160 degree thermostat. It ran pretty good and was staying nice and cool, although I did have to add coolant a few times in small spurts. But then after adding 5 times it seemed to settle down and be right. Then I developed an oil leak out the back of the intake gasket and had to re do the job. My fault just didn't put down enough RTV.

Now it seems that after about 5 miles of driving the engine starts running hot. I am thinking that the 160 degree stat is not closing and letting the coolant actually get cooled in the radiator long enough. So I got a 180 stat and the same thing. The engine will warm up, get hot and stay hot?

Is the water pump not pushing hard enough anymore? Will a 350 run without a thermostat? I wanted to try that one anyway with some cleaner in there and see if I can get rid of the DEXCOOL sludge, but haven't yet because I would like to figure out one problem at a time.

Any suggestions will be appreciated. Thanks Rich.