Depends on tire size, etc... I say go with the 14 bolt full floater for strength... lol

 

how can i tell it is whatever came stock on the 4x4

 

Decode the RPO code list in your glove box.

For gear ratio & differential options:
GU4 Rear Axle: 3.08 Ratio
GU6 Rear Axle: 3.42 Ratio
GT4 Rear Axle: 3.73 Ratio
GT5 Rear Axle: 4.10 Ratio
G80 Rear Axle: GM Gov-Lok Automatic Locking Differential

Or mark the driveshaft and the front of the differential with an alignment mark. Mark the wheels at a location where you can judge one turn. Then turn the driveshaft counting how many rotations it takes of the driveshaft for one rotation of the wheels.

 

I just read this and I know nothing about rear ends but I was wondering right now my truck has no power at all and Ive been told to get a new rear end or change my gears. I dont know what is in mine right now but I know its stock and Its a 99 4d base if that helps. Id really like the get the power out of the motor I put in it.

 

Find one of the codes above on the RPO code label inside your glove box.

And even with 3.08 gears, these trucks are not really gutless... You need to fix the problem you have before dumping money into other things.

 

Ill look and see what i can find on it.

I dont really know what is wronge with my truck Ive takin it to alot shops and they have looked everything over and say their is nothing wronge but It seems like their is something making me loose power.

 

I don't know if this is really relevant to this thread, but I recently changed out my rear end. I had 3.73 gears according to the rpo code. The original rear end was not a limited slip rear end. The one I put in is a limited slip. I've noticed I get passed a lot on the highway now, and recently passed one of those radar signs that tell you how fast you're going, and I was going 55 +/- 1-2 mph according to my speedometer and 50 according to the radar. Anyone have any idea what gear ratio the new rear end is?

 

Sounds like you got a 4.10 rear end. Unless you are running tires that are 10% smaller than stock. 4.10 gears will lower your actual ground speed by ~10% at a given indicated speed on the speedometer when compared with 3.73 gears.