Gear ratio?

I don't understand the problem with figuring out what the gear is by turning the drive shaft. If you lift 1 wheel preferably the right rear. put a jack stand under there BE SAFE and mark the inside of the tire now crawl under and turn the driveshaft and see how many turns it takes to rotate the tire 1 revolution. 3 1/4 turns = 3.23 just under 3 turns =2.94 2 3/4 turns =2.76 just under 4 turns = 3.91 its not that hard. u must turn the driveshaft it dosen't work the other way.
That said if u are going to do a lot of 65+mph driving I would go with a 2.94 or 2.76 Ijust removed my 3.91's after just a few miles because it just turns to many rpms for me at 70 close to 3500 with 27" tires. I'm puting my 3.23's back in but if I need to drive long distance i will put my 2.76 in or If I get real enerjetic I will put my O/D in with the 3.23's. I don't think I'll ever use these 3.91 again so if some one is looking I have a nice tight quiet 742 case 3.91 suregrip for sale.