I'm as green as a newbie can be. Looking to by a 96 Ram 2500 SLT 4x4 Cummins with 160K miles as a tow truck for a 10,000# 5th wheel. It's been taken care of but I know that's a lot of miles on a stock tranny. I have to assume I'll have to have it replaced or rebuilt by 200K miles.

What's a reasonable cost for a major tranny overhaul?
Should I consider having it replaced with an Allison (I've been told that conversion kits for that are available)?
Other advice?

thanks
Jerry