The SOB's at Freightliner El Paso accomplished almost nothing in spite of charging a great deal and wasting eight days of my time. I got almost to Deming, New Mexico and had a sidewall blowout on a front tire. That took two full days of screwing around to get a front tire replaced. And to get the other tire replaced as well because of cracks in its sidewalls. I had the air filter replaced. It was clogged and changing it significantly improved the performance of the engine. But it still spontaneously shuts down under heavy load, i.e. highway speeds. I had assumed that fixing the air filter and thus the air pressure problem would also fix the shutting down problem since I assumed that the engine was being throttled off by too little air.
Now I have no idea at all what the problem is. I drove back to the mechanics shop in Deming that changed the air filter (it is a huge cylinder and hard to get to). They said that they didn't do such work and that I had to go to an RV service department to get it fixed and the nearest ones were in Las Cruces. So I backtracked fifty miles to Las Cruces. And learned the exact opposite. The RV service department I spoke to said they did NOT do that kind of work. So my trip to Las Cruces was pointless. But since I am here I am going to talk to yet another mechanic tomorrow. So it goes on and on. I cannot see a way get out of this without solving it.
While it is discouraging and dispiriting, it is still true that I have gotten three of the problems fixed: the tailpipe, the air filter, and the tires. If I can get the engine shutting down problem fixed, I think I can go home.