...and since I was all worked up from getting to spend an afternoon on the rig, I may have figured out the cause of my jumpy speedo.
Disconnected the sensor and no jumping, so the problem is likely there and not some sort of short or interference further down the line. Decided to check on JB Conversions website about which sensor is used as I can't seem to find the same one on-line (some Honeywell OEM Chrysler sensor)....and they have a big note in their install instructions about tightening the super short nut to 200 lbs. torque. If not, it may cause erratic speedo.
If that's not it, then I guess it is a bad sensor....easy enough to replace, but I would rather it be the free fix....we'll see....