I have a 2000 Chevrolet Silverado 5.3. I can drive out about 3 miles and it looses power lugs out and when i kill it i see steam and boiling water coming off of my overflow tube coming out the side of my reservoir tank. So i let out sit another 10 minutes i can crank out and drive about another 3 miles and the sake thing happens over and over everytime. I mean add long ad i have water to put back into the reservoir that is...i have changed the thermostat i have flushed the block i have put a new coolant temp sensor in i flushedd the radiator andcant seem to get it fixed what is causing it to run like that after i go the exact same distance everytime i don't understand what's causing it to do whatever it is that is doin . It's kinda like it's goin limp mode after something. Please help me eith this and thank you