[CWizard]

After some discussions with Tremec tech support and some other Cobra owners, I removed the tunnel to allow access to the top of the transmission. Removed the inspection plate just in front of the shift tower and found the tranny stuck in 2nd gear. Used a screwdriver to unstick it (had to disengage the clutch first). Problem fixed. Except, of course, putting the interior of the car back together. But why did it stick??
My fellow Cobra owners tell me this lock-up can be caused by bumping the shift lever while the car is parked (engine off) and in gear. Apparently it can happen in any gear, although 1st, 2nd, 5th, and reverse are more susceptible. That is reasonably consistent with info from Tremec, who concluded my problem was likely "creep of the shift finger to the point it escapes between the shift gateshaft", and recommended parking only in 3rd or 4th (or neutral) to avoid recurrence.
Hope this is useful to some of you Tremec owners.