2001 Chevy Astro running Hot

The Astro run hot the same after I replaced the thermostat and cleaned the radiator. So I took off the water pump to make sure it was pumping and the fenns in the pump are still good, so is there any other thing to look for that would make it run hot within a half a mile ride.
Now I have taken the thermostat back out and ran the van for over 5 miles with out it and the temp stayed where it should have around 190. So I went got another thermostat because it ran hot with the new one and put another new one in and it runs hot with this one as well. So the bottom line is it the motor will run without a thermostat but runs hot with one now.