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.