Low coolent in 99 4.3?

I have a 99 Silverado with the 4.3 V-6, and it is constantly low on coolent. I add a gallon, and within 2 days the low coolent light is on again. I haven't been able to find any leaks in the system, and there is no coolent in the oil. I do occasionally find some underneath the truck, although not in a while now. I replaced the reservoir tank cap, thinking maybe it was leaking around that, but it didn't help any. Anyone have any suggestions? Thanks. Sparhawk56.

I also Have A silverado with A 4.3 v6 with the same problem. I figured it out one morning while the truck was warming up. It was the water pump.When you start the truck up it would not leak let it sit and run for A couple of min and I would start to see A steady drip comin from the weap hole of the water pump . Took it back to the dealership naturally it was out of warranty so they didnt replace it. The truck only had 37k miles when the water pump took A dump on me.Took it to another mechanic and they charged me 200 bucks to fixs it.Mechanic told me this was A commen problem with chevy water pumps. I love my truck but I will never buy another one,too many problems with the new body style. Hope this helps