speedometer going crazy on 94 LE w/ 3.1 V6 /Auto

[newsboy837]

ok so yesterday the speedometer on my 1994 Pontiac Sunbird (LE 3.1 V6 Auto 2 Door) started twitching. it gradually started swinging 10MPH below the speed i was driving. i had about a hour drive home and it just stayed doing it, gradually getting worse. since then it is still going crazy and now it is completely normal untill i hit around 40MPH then it will swing between 30-65MPH when driving around 65. if i let off the gas it will swing to ABOUT what the actual speed is but it shifts between gears constantly when it swings from high to low MPHs. in the past it has twitched a little every now and then but never like this. i am thinking it may be a ground somewhere (it seems worst when on bumpy roads). any advice on where to start?

 

[DanSavage]

Speed sensor

On the tailshaft of the transmission(passenger side) is the vehicle speed sensor. Look for frayed wires, or broken connector, if not, make sure it is seated if seated, replace it.