[Zeke3]

I agree with Juergen's advice. You didn't tell us what size rear tire you plan to use, but the 3.54 axle will be better for the 65 mph cruising. A 3.78 axle with a 28 inch diameter tire calculates out to 66 mph @ 3,000 rpm. With the 3.54 axle, the same 66 mph can be achieved at a little over 2,800 rpm.