The engine RPM is 3417.35 at 65 mph.

A few calculations on the way:

sidewall height = .8(165mm) = 132mm = 5.1969in
wheel diameter = 13in + 5.1969 = 18.1969in
wheel radius = 9.0984in

v = r*w
65mph = 9.0984in*w
w = 125.74rad/s = 1200.6908RPM

After going through the differential:
w = (37/13)*1200.6908RPM = 3417.35RPM

Since we previously found the gear ratio of high gear to be 1/1, the engine will also be running at 3417.35 revolutions per minute.