A gear vendors is just as expensive as a 4L80e. If you go new. Rather you buy used new or rebuilt.. Plus it has a 20% overdrive vs a 30% of the 4L80e.
Plus it would not have a lock up converter which I would want if I wanted a real tow pig. So my choice would be a 4L80e.
https://www.car-part.com/mobile/index.htm
Is a good resource to help find parts, and often cheaper then ebay.
Forgot to add. If you switch gears to get good highway manners. You loose to much pulling power. The 4.56's are to me perfect with a 4L80e, and 30" tires. You will be about 2500 rpmat 75, and have enough air flow over the carb to get optimal mpg.