You can pay a shop to put a shift kit in or you can buy a VB that's already done and install that yourself, probably going to end up comparable in price...I think you're better off buying a VB from a reputable diesel trans place like Georend or Suncoast that has thousands of repeated good results. Any transmission shop will tell you "yeah I know all about those dodge cummings transmissions and I can put a shift kit in that thing for you...". And yes, I learned that the expensive way.

Contact both Dave Goerend and Suncoast and ask them if they have any dealers or can recommend a trans shop nearby. Dave's used to talking to transmission shops and going over specific details with them if he doesn't have a vendor in your area. It's really not terribly difficult to do yourself, it takes far more time to get the trans out and back in than to do the actual parts installation.