I've got a 99 maz B4000. I know they made then with 3.73 gears and also with 4.10. I bought it used last year- how can find out which mine is- I've exhausted my resources.    

Simply jack up one rear wheel with truck in neutral and turn wheel exactly on turn and count drive shaft revs and multiply by 2 and you will have gear ratio. (spider gears double drive shaft speed with one wheel stationary)  

It's easier than that even. Crawl under and look on the tag on the rear diff. It will say what the gear ratio is. Something like "3 73 88" which would mean you have 3.73 gears and an 8.8 axle. or something like "4L10 88" which would be 4.10's with a limited slip. Follow?  

This is a good point but tags are not always present.  

Unless the cover has been removed and the tag lost, these axles have them.

You could also look at the axle code in the door jam, it is a number/letter code in the box marked AXLE. Simple google search will decode that.  

Follow!!! thank you for the info- forgot i had posted- found the tag it has a 3.73 limited slip (3L73 88). I didn't think the 3.73 came with limited slip, that's why I originally just assumed it had 4.10's- The limited is still tight and you can feel the "slip" starting off in a turn. Guess I can't go with 32-9.50-15 (stock suspension)not geared for 'em-  have to stick to a 31-10.50. I've done my homework on tires and I have my tried and true favorites from lots of wheelin' -- looking to go more aggressive(to satisfy my cravings) but with street-ability- "daily driver"- ANY SUGGESTIONS? Thanx, again

oh, and you too snoman  

FourWheeler Web Editor:
It's easier than that even. Crawl under and look on the tag on the rear diff. It will say what the gear ratio is. Something like "3 73 88" which would mean you have 3.73 gears and an 8.8 axle. or something like "4L10 88" which would be 4.10's with a limited slip. Follow?

Follow!!! thank you for the info- forgot i had posted- found the tag it has a 3.73 limited slip (3L73 88). I didn't think the 3.73 came with limited slip, that's why I originally just assumed it had 4.10's- The limited is still tight and you can feel the "slip" starting off in a turn. Guess I can't go with 32-9.50-15 (stock suspension)not geared for 'em-  have to stick to a 31-10.50. I've done my homework on tires and I have my tried and true favorites from lots of wheelin' -- looking to go more aggressive(to satisfy my cravings) but with street-ability- "daily driver"- ANY SUGGESTIONS? Thanx, again

oh, and you too snoman