Custom gears...

[GasSavers_Ryland]

I would guess that to modify a tranny to a higher 6th gear is going to cost you ALOT of money, money better spent on a differnt motorcycle, just because your current motorcycle was free doesn't meen that it's practical to make this change.

Sell your motorcycle, and buy a differnt one.

[DRW]

Talk with the guy behind the parts counter at the motorcycle dealer and see if they made different models based on the same shaft drive system. Maybe there was a touring version that had taller gears? Sometimes manufacturers will use the same cases for different models to spread out the costs, so the internals may be compatible and swappable.

[omgwtfbyobbq]

This would be an all DIY job with the help of my uncle if possible. Looking for a taller set is a good idea too, and hopefully someone will have something.