My tahoe runs great other than the fact that it sounds like water sloshing in the heater. I had this problem last year, and it was because there was bubbles in the coolant after it had been refilled. This year, it sat for about a weak, and I noticed a leak coming from the transmission cooler screw on the radiator. There is again a sloshing sound in the heater, and now it only runs on high. Any help or suggestions would be greatly appreciated.

 

Your heater should be full of coolant. If not, that is why it's sloshing. Something is blocking the coolant. Might be a bad hose or the inner portion has deteriorated to the point of its blocking a good coolant flow.