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I'd suggest calling Criswell and asking to speak with Bob Wisman who is the Service shop foreman. Bob also is an accomplished road racer that knows C5s very well. Tell him your symptoms and ask if he thinks Criswell can solve the issue. If he says "yes," believe him.
Ranger
I think I'm going to do that. The dealer can't figure it out and now wants me to take the mechanic for a ride. Did some quick research and I've found one complaint on this very problem at NHTSA's web site
It took 6 trips to the dealer, but "Ask the Mechanic" crossedflags.com figured it out. It was a steering wheel position sensor. The car never threw a code despite the anomalous data coming from the SWPS.