Gearing question

[Rolson]

I have put an MB OM617 with a Jeep AX-15 in my Ford Ranger.

The AX-15 came with an electronic speedometer output, and the Ford uses a mechanical cable. I talked with a guy at a speedometer shop. I told him it has a 3.47 rear gear ratio, running 215 70R/14 tires. According to 1010 Tire they are 25.85 inches tall.

He told me I would need a 35 tooth output gear, with a long shaft, and the cover plate.

I found one on ebay, and installed it. According to my gps unit, it is 3 mph off at 60, and 4 mph off at 70. I trust my gps as it is accurate on the other 2 vehicles we own.

I need to clarify: The truck speedometer says 60, the gps says only 57. When the truck speedometer reads 70, the gps says 66, so I am reading faster than actual. What do I need to get, a gear with more teeth, or fewer teeth to slow it down?

Thanks.

Rick