When I added afew upgrades, stock converter starting slipping. This was at 98K miles 3 years ago.
Before it clogged the V/B, I decided to add an ATS triple lok converter. When local transmission shop said for another $500, we'll rebuild it stock for towing. They did not believe in increasing line pressures.
Anyway, truck has 150K miles now, only pulls the 15K fifth wheel, and seems to work fine still to this day. I even have slightly larger tires and 355 gears as well.
I think you'll be fine if you drive it right.