It was made clear to me that if I turned down the tow and it turned out that I need a tow I would have to pay for the tow. Fair enough I said.
I asked which of the Road side service places was the most expensive they gave me the name and I called him. He showed up with full diagnostic computer gear and after some time diagnosed two problems, a sensor and a clogged fuel filter. Pretty much what the Cummins center 60 miles away would have done.
IMHO I'd have opted for the tow. Doing mechanical repairs on the side of an interstate is risky business and many shops won't even allow it anymore due to insurance. Its a real **** shoot if it even CAN be repaired roadside and then there are the parts needed to do the job. They sure can't carry every part known to man on board. So for me the odds are against it so I'd rather be towed off the road for safety reasons. Deal with the fixin later.
Glad you were lucky enough to have it fixed right there!
You said you asked for the most expensive tech service.
Did YOU pay for the call or did GS pick up the entire bill?