This would be weird, but I wonder if the lever is flipped on the 3-4 fork? That would give you 3rd gear when you thought you were in 4th and would put your RPM at about 3750 at 60 mph with a 245/60/15.
I would think it would feel weird, and be dangerous if you RPM'ed the motor in 1:1 and then shifted to 1.39:1. But it's the only thing I can think of.
But we will know more when you post some numbers.
