I had that same problem back in the summer. It was leaking. I had to get an entire Tank on the passenger side replaced because it had cracked, Then Split about 5"s and finally blew a hole on the freeway. Just DONT let that puppy go dry I don't care if you have to fill it every day. If you have a leak and if it's a minor one, Head up to autozone and get some Bars Stopleak for radiators, Get the Silver Colored stuff and put about half a bottle in your truck while the truck is off, Then, Fire it up, let it run for about 20 minutes and see if it still leaks, If so add the rest. That should stop any minor leak. but just remember to take it to a radiator shop and find out what the real problem is.
My only limit is my straps