work with the dealer - not Isuzu. Isuzu has nothing to lose - the dealer has his reputation at stake. A dealer will normally protect his name and reputation if given the opportunity. You are NOT making an unreasonable request - you are only asking that your vehicle be repaired under the terms of the factory warranty. You are the customer - you bought a vehicle with the understanding that if it had certain issues within the warranty period, the manufacturer's dealer network would stand behind it. You took it to one of their authorized repair facilities - if they did not repair it to specs, IT IS NOT YOUR FAULT - it is the fault of Isuzu. Call the dealer Principal - tell him about your trials and tribulations. Tell him that you don't want to go to the media to get your problem resolved, but you will do what you have to do - you spent all of your money on a vehicle that you assumed would be backed by the dealer/manufacturer.
At this point, it doesn't matter that the dealer in question is not the one who sold you the vehicle - he is the dealer of record and the "responsible party" as far as everyone else is concerned. BE BOLD - DEMAND WHAT IS DUE TO YOU!!!!! You are the consumer(customer)