2016 Freightliner Cascadia - Nightmare OneBox Replacement

Good morning, truckers! I apologize if I am posting this in the wrong area, but I would greatly appreciate advice on this nightmare of a OneBox replacement. I am posting this on behalf of my father, who owns the truck. The details of the truck are below:

Make/Model: 2016 Freightliner Cascadia
Last 8 of VIN: GSHF1649
Approximate miles: 532,000
Engine: Detroit DD15

To start, my father bought this truck around May or June of last year. The truck was still within its period of the EW3 warranty, but we also tacked it on with the EN4 warranty. By August, we were having issues with the truck constantly shutting off and refusing to drive. We took the truck to our local Tag Truck center in the same month (, and after many diagnostics + replacements (DPF filters, Aftertreatment sensors, Injectors, Injector Cups), it was determined the issue was with the OneBox.

This final diagnostic was back in November of last year. As a note, they were mostly sure it was the OneBox from the first time we took it to them, so we kicked off the EN4 warranty then so that everything would be covered (OneBox is not covered under EW3). The reason it took them 3 months to make a "final diagnostic" was because we were doing this all under the warranty, and Detroit was taking a while to respond, constantly asking for more diagnostics.

Here's my issue. The OneBox is still not here. We've been on back-order since November, so around 5 months now. The original date for the delivery of the OneBox that they gave us was January. It was then pushed back to February, then to April, and now it is "Unknown". I wanted to ask a few questions regarding that:

1. Are these One-Boxes so high in demand that it would actually take that long for it to come?
2. Is there anything I can do to expedite this process?
3. Is it even worth it waiting for the OneBox, or will it just break again immediately?
4. If the warranty ends (in August) before this issue gets fixed, will I be responsible for all the payments?
5. When I tried to take my truck to another dealer, they said that I had to pay $7,000 for all the labor done so far. Is this common?

Thank you.

---Edit---
Here is also an easier to read timeline:

May/June 2021: Father buys the truck
July/August 2021: Truck stops work, so Dad takes truck to mechanic. They say it may be OneBox. We kick off EN4 warranty.
August-October 2021: Many diagnostics and parts replaced (DPF filters, Aftertreatment sensors, Injectors, Injector Cups)
November 2021: They inform us it is definitely the OneBox, and set a date of arrival for January 2022.
January 2022: Part does not come in, gets pushed back to February.
February 2022: Part does not come in, gets pushed back to April. We try to take the truck out, but they say we must pay for all replacements done so far, as warranty will only cover if the truck gets fully fixed.
April 2022: Part does not come in, delivery date gets pushed to unknown.

 

He spoke with the TAG truck center yesterday, and they actually informed him they may be able to get one from Dinex, but he would have to pay $2000 out of pocket. My dad just wants it to be fixed at this point, so he said sure. We’re waiting til tomorrow to see if they will allow us to do that. Thank you for the suggestion!