Loss of power in reverse - I have a 2007 Silverado crew cab Z71. I recently purchased a camper that weights about 4500 pounds. I backed it up my driveway ...

I have a 2007 Silverado crew cab Z71. I recently purchased a camper that weights about 4500 pounds. I backed it up my driveway which is pretty steep. It made it up, but about halfway up it started to make a grinding/sqeaking noise, and wouldn't move. I went to the bottom and tried again gaining more momentum this time. It went right up it. Saturday I got back from a family trip to the beach with our new camper. When I tried to back it up the driveway this time it wouldn't do it. The truck would push it up the begining of the driveway, and then just stop making the same noise as before. Of course the camper weighed more this time because it was loaded. I unloaded the truck and camper at the bottom of my driveway, and was able to get the camper up, but just barely. Now my truck makes that sound if I back up my driveway completely unloaded. It seems to have had no effect on any of the forward gears. My question is one, what damage did I do to the truck, and two why is the truck having so much trouble with this camper? It is well under the tow rating. Thanks for your help

Do you hear the same grinding in low gear? I think the transmission is toast. How does the fluid look? Did it smell real bad?

No I don't hear the noise in any of the forward gears. I have been driving the truck for the last three days with no problems. It will go into reverse fine and backup as well. But if I try to back up my driveway (steep incline), it will make that sound. Just a little. The best way I know how to describe it is it sounds and feels like a belt slipping. But there is no high pitch squeal it's more like a low pitch sound. The fluid looks fine and there is no bad smell.