^^
The fleet I work on had a couple of Sprinters with that
Same eng/trans combo... Trans failure was the biggest issue
(usually about 80k miles!).
Engines usually went 200k or so... but then those miles are
UPS miles ... lol, so double that & add a 100% abuse factor.
NV3500 will be a good upgrade, as yokes, u joints, & drivelines
are plentiful. might even be a 'drop in' driveline around.
Again cudos I love these 'push the corner of the envelope Budget minded builds'