Like I said, I'm not sure if the engine is still revving while the tach is strying to catch up, or whether the tach accurately reflects the RPMs... it goes by so fast I suppose running through 2nd and 3rd gears would help to diagnose this, but I have to go about 20 miles from home until there's a non-rural highway

My tach did the same thing. Slowly got worse until it quit one day. Had it worked on at a tach repair shop $40 bucks later she's all together and working again.

hmmmm... I'll keep that in mind... $40 at a generic "tach repair shop"? I don't know if we have any of those around here... :-)

Look in your local phone book in the automotive section, you should find something in the speedometer or electronic repair section.

Thanks!