Problem solved (if anyone is interested)
I had hooked up a spare tach for testing as I went out for the mileage test. Just tossed it on the seat. This morning when I started it, It said the idle was high, but it wasn't.
The cylinder selector switch had gotten bumped into the 4 cyl mode.
So the "3500" was probably 2700 or so.will recheck it and am pretty sure it will be much closer to the odometer error.