Speedometer problem?

Transmission problem 6 cyl Front Wheel Drive Manual 76000 miles

I had quick onset of problems with my speedometer. Within the last six or seven days the speedometer needle would "slip" slightly and read lower momentarily (e.G, it would "slip" to 35 or 30 when I was going 40). This has progressed over the last week or so to the point that the needle would slip dramatically (e.G, from 60 to 45 to 30 and then back up in a similar manner to 60 again). Eventually, the speedometer needle just fell to zero while I was driving, I got an "error" message on my digital odometer, and the engine light came on. Now the needle recovers very erratically and the engine light stays on.

As far as I can tell, I've had no corresponding engine performance problems (e.G, no loss of power, no revving, etc). The only other thing I've noticed is that the automatic volume leveling feature on my sound system has fluctuated along with the speedometer needle. Thanks VB