No love for the NV3550. In my never ending quest for a higher crawl ratio I would have a hard time giving up the taller 1st gear in the NV3550 (4.01) over the AX-15 (3.83). Personally I would put a 3 speed auto in before another manual but that's just because I've been playing in the rocks a lot lately.
@RJPen have you called any transmission shops and gotten a quote to get it rebuilt? If you're considering a swap I would assume you feel comfortable pulling the transmission out yourself which should save a good amount of labor.
Most likely I'll be pulling my transmission out this winter since I'm fairly confident my throw out bearing is shot. (ticking noise while in neutral and the clutch is out). While its out I would be an idiot not to change the clutch. 105k and no service history.