Jagmandave made an excellent point. Document, document, document!
If you have not done it already, get you a notebook. Log the time, date and info from every phone call to the dealer, trip to the dealer. Log every conversation you had with the NH Rep. Make sure to note who you talked to. Note each trip you made to the dealer to check on things. Log what else you have bought from the dealer, when, ect. Start from the date you bought the tractor, and keep it up to date and current until all this is resolved.
If you have this data already, you might go to your dealer.Tell them you've been in X amount of times, been without your $20,000 tractor X amount of days. You want resolution right away...
Check your state Lemon law stuff too. Use that info in conjunction with the above info in your talk with the dealer.
One other thing to log, and to point out to the dealer and the NH rep... Note any and all time you have had to take off from work to deal with this...
As for the parts, that's bogus. My Dad has worked Mopar parts for years. Sometimes a wrong part is shipped, or is backordered... But that is not very often. And, it is not a big deal to get that stuff resolved.