1993 Toyota Camry

Transmission problem
1993 Toyota Camry 4 cyl Front Wheel Drive Automatic 210000 miles

For a little while now i've had the problem of my speedometer needle randomly jumping around when I wasnt in motion. Then engine didnt rev or anything, the needle just jumped around. A couple of weeks ago, the speedometer finally stopped working all together, so the odometer isnt rolling over. Now when I try to drive it, the transmission is lagging and is having a hard time changing gears like normal. The problem seems to be better, although still not normal, when the overdrive is off, but when overdrive is on, it wont switch gears at all. What would most likely be causing this, and is this something that can be tested/repaired myself?
August 26, 2008.

Have the vehicle speed sensor sender unit on the right side of transaxle case near right axle shaft inner joint checked out-

Aug 26, 2008.