It sounds like your mind is made up. Go with the 1500, I don't think you will see 10mpg out of a 2500 though. 13-14 yes, 10 no.
One thing I'm am sure on is don't believe the I pull 7k lbs and don't know it's there crowd. My neighbor regularly goes with us to the lake. He pulls my 5k boat and trailer behind his 15 gmc 1500. He gets 8.5 mpg and can't hold a hill without the truck Erving to the ceiling and falling behind. So yes it will pull your trailer, probably hundreds of thousands of miles. But you WILL, know it's back there and you will be exhausted if traveling a long distance. Every hill you come to will require a lot of pedal and down shifting to minimize speed loss.
I'm not bashing anyone's decision to purchase a truck that fits their needs. I'm just being real with you. It will pull it, you will be close to its capacities and you will know it's back there. That's is all I'm saying.