1998 Plymouth Voyager 98 Speedo starts at 30mph and goes fr

Hello. With your help I've already found the back ground solder connections on the back of my dash, also fixed the blinking lights for my heater controls. NOW. I'm back for more help.

I replaced the Trans roughly a year ago, repaired the dash ground connections about 5 months ago, now when I start the van the speedo jumps to 30mph while in park. The speedo seems to work fine, it just starts at 30 and continues to go from there. Basically 30 is the "new" starting point.
Any thoughts. Wonderin if pulling the battery off for 15 minutes to reset the computer would help?

Thanks. And again, great site!

Jery