Frits wrote- I'd give you the advice to have the dealer pick up the truck and say you don't want it back when it drives OK.

If I would have such a problem with a costumer I would also pick up the truck. In the workshop, without costumers around, and with help of collegues, and when lucky an other truck of which you can borrow/exchange some parts these kind of errors are better to deal with.
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Good advice. I tried to get them to do that but they say it won't fit in their service trucks and requires a large truck to pick up and deliver and therefore costs less for them to repair on site.

Which would be fine except they tried and failed at that.

To my amazement, even with definite proof the truck has a serious problem, they are back to ignoring me.