4.11 seems probable. How are you seeing the driveshaft spin? doesn't your 1/2 ton have a torque tube?
try spinning the wheel twice or even more like 20 times and then devide by 10. sounds complicated but it isn't. the spider gears are taking up 1/2 the travel. so if you spin the wheel twice, you will get a more accurate picture. 20 times even better.
