diff ratios

if i turn one of my wheels front or back with the opposite side still on the ground and the transfer box in neutral ,i get @ 2.5 turns of the propshaft for one complete rotation of the wheel (7.50 x16) does this sound a lower ratio than a standard ( 90 axle i think) just wondering because the engine seems to be ready to explode at approx 45 mph,its a 88 inch with a 2.5 diesel in it and sat on a coil sprung "designa chassis" any help appreciated
cheers

The standard 88 ratio is 4.7 to 1.
With 1 wheel grounded, the opposite wheel should revolve once for every 2.35 revolutions of the propshaft. I would check again with accurate paintmarks in order to be absolutely sure that you've got 2.5