I guess I would add in a couple thoughts here,
When they are working with you, and everythign is going well, it is very easy to just kind of keep going, OK, OK, that's great.
But I would suggest, and you are probably already doing this. keeping yourself a small log book / diary, of the conversations, phone calls etc.
If it were mine, and I had that much $ rolled up in it, I would write what the rep said in my little log book, and ask him to sign it after Friday, or ask them to write it out. Kind of a mini contract.
When you have to go back two months from now, and you say,,, "I spoke with a lady at Corporate" or you say, "I spoke with Ms. Ophelia Smith at 123-567-3456 on 18 July 07" it carries a bit more weight.
I sure hope NH gets you going again and turned around.
I would be furious.
I had engine problems out of one of our commercial mowers once that took a bit. It finally got to mowing season and we were still getting jacked around as to if it was warranty or not (multilayer thing for kohler)
I finally got the head warranty guy for Kohler on the phone and said flat out
"Look, this thing has to run for me to make money to make the payment with. I need you guys to make a YES OR NO decision if you are going to support this or not and when you will get it fixed. If it is not warranty, that is fine, I understand that, I will kick this motor off, put on a Kawasaki, and see you guys in court later, but right now, I have to go mow so we do not go Bankrupt."
They got me a new Pro 23 installed the next day.