All of the following is PURE opinion on my part. Take it or leave it:
This is going to sound crazy but we always had VERY good service at Cummins in Avondate, Arizona (Phoenix). They charge top dollar- I think their labor rate is somewhere around $110/hour. We got to the point where we wouldn't take our truck anywhere else unless we had to- there are plenty of mediocre and bad shops out there so we've come to appreciate a good one.
Every time we had something done there, they stood behind it 100%. We only had an issue with workmanship once- and that was on our generator, and the situation was one that really wasn't workmanship, it was a parts failure of a part they hadn't replaced and we had made the call not to replace it when they had the generator torn apart. They felt responsible for not having required us to replace it and gave us the part at cost (probably still made a profit on that) and put it in for free (it was a full-day job to get the generator out and torn apart to replace it). Any engine work we had done there was always top notch.
I can tell you some Cummins dealers to stay away from, too, though...
If you're going to pay top dollar for a rebuild, don't go to the KW dealer- go direct to a Cummins distributor (not a Cummins authorized shop- an actual Cummins-owned distributor). The Cummins guys work on Cummins, train on Cummins, they know Cummins. If you go to KW, you're liable to have the a/c guy doing your inframe.
There is definitely something to be said for a mom & pop shop that does good work and doesn't take your wallet with them when you leave... For an inframe, though, unless you KNOW the mechanic is qualified/good, I wouldn't risk it personally.
There are quite a few states that
don't charge sales tax if you have an ICC number (leased to a carrier counts)- Ohio, Indiana, Pennsylvania... not a bad idea to save some $ on sales tax on parts by going to a shop in one of those states.