Hi Mike. I can tell you that my speedo is off too. It is reading about 2mph faster than the gps at 60 mph. Mine is due to a bit smaller tire size in the rear. When I had it at an Allison shop a couple yrs ago for a fluid and filter change, I had asked them about taking care of that issue and they said they wouldn't touch it. The down side is that it racking up more miles on the odometer than there should be.
Steven USCG EMC Retired
Lilli Pi(the crazy cat)
1998 Country Coach Intrigue 2000 Jeep Sahara w/Stay in Play Duo