Did I mess up?

[Jerrod]

The friend I have doing the body work when I have money has a seized up4.8/5.3 he said I could have for 200 bucks. Is that a good deal? I think I want to go bigger than a 5.3 though. I will do some towing, lots of deer hunting in it. I was hoping to get around 15mpg when all is said and done. That's why I was thinking corvette, if I could get 350 horse with 15 mpg I would be tickled pink. I have been thinking going with the 6.0 backed up by a NV4500, or get a gear splitter on the 4 speed. Is 15mpg out question with a 6.0. I don't need anything radical either, relatively stock is just fine.
My wife and I are going to refinance our house to do our kitchen and maybe a bathroom, so I told her I was going to take out some more to put into the suburban, it is only going to appreciate right. The crazy part was she said okay so I have to get it done before she changes her mind, haha.
Thanks for all the responses, everyone has been great. Cheers