The 4L80e is essentially an updated TH400. Both of which are considered to be among the very best transmissions of all time.
There is a reason the previous owner wanted to get rid of the vehicle. They probably did something stupid and wanted to get rid of it before it failed completely.
Get your transmissions rebuilt and you should have no problem. Just use a reputable transmission shop (do your research) and make sure they understand the vehicle characteristics, and your intended purpose.
Go ahead and google it. The 4L80e is practically God’s transmission - it’s that good.