Used Truck purchased but has been in the shop for nearly a month

[Bali Hai Again]

If I would have known that this truck had major transmission issues, I would have put 2 and 2 together and assumed that the previous owner beat on the truck and likely abused the engine as well and therefore I would not have purchased it.

You are getting a brand new tranny. If you are worried about the engine have them put it on a dynamometer after tranny replacement. At the least you have a truck with 23k miles with a new tranny under warranty and extended warranty.