1997 Plymouth Voyager jerking car and wild speedometer

This is EXACTLY what is happening with my 1992 voyager. Its been happening for months, though I still drive it. Mostly on hills, and getting a tiny bit better now that the weather has improved. But still up to the same ol antics.
I'm still searching for answers, and haven't solved anything yet, but have been told recently that it could be the speed sensor.
These vans are equipped with a 'govenor', and when the speedometer is reading over 180km/h the van wants to cut out, and not let you go any faster.
This has been the only answer which makes sense to me so far, so its worth a shot for me. I'll be trying this as soon as I get the part. I'll let you know how it goes.
Good luck.