Hi mate, shift kits are sick I'm running a stage 2 in my VN. but you might find that if you run that one when you drive in normal gear it will drag the gears out longer. shift kits start from about $350 or fitted is around the $500 mark.
Depends on the kit- the B&M Shift Improver (commonly refered to as a shift kit) can be had for $80 from Rocket Industries. I believe it makes changes effecting the oil pressure in the box which then firms up the shifts. I'd look into a new billet servo to really thump it into gear.
There are other kits out there- Transgo etc. aswell as modifications done by certain trans shops- which vary in complexity, function and how they affect your daily driver. But the B&M seems the most common. Just keep in mind that a properly installed shift kit won't damage the box unduly but if the box is already in not the best nick, it may kill it in record time.