2003 suburban rear end
 

I just bought a 2003 with a bad rear end, got it at a great price and my father is a mechanic. However he is pulling out what hair he has left with some gear issues. He has many rear end guts and none seem to be working. Any advice???? what years are interchangeable?

The 03 is Tenth Generation, that being the years 2000-2006.

One could just buy a complete Rear End out of a Wrecking Yard, and just bolt it right in.
However, within the various applications, there were several Gear Ratios which were installed, some which included Limited Slip* Differentials. That type Differential would be a nice addition, if your original didn't have that.

If your vehicle is 2WD, a ratio change would be possible.
If your vehicle is 4WD, then you must replace with the original Ratio.

* = There are other terms (Positrack/TrueTrack/Automatic Locking) which may be applied to the/that type Differential.

Could you be a bit more specific on the troubles your Dad is having ?
Also, could you look at a Tag in your Glove Box, and post all the three character/number codes you see there, starting with the letter "G".

its a 373 gears with positrack and a gt4 also g80.

RPO Code GT4 - RPO Code G80
 

Amanda,

Yes, those check out...

The 3.73 ratio is identified by the RPO Code GT4.
That's a very popular ratio, mainly for Street/Hiway/MPG.

The Eaton Automatic Locking Differential is the G80 code.
This type Differential has a mind of it's own. It changes from both wheels Locked together when you start off, and about 20 MPH it unlocks automatically. That's a very efficient MPG enhancer.
(I have both of these in my 03)

But, back to your problem...
If you can, try to explain just what trouble your Dad is having, maybe we can come up with some sort of fix for you.

I (cautiously) will add...
I'm sure your Dad is a great mechanic, but, it takes a "knack" and proper tools for repairing Differentials. Often times, those who may not have much experience with them, do not have good results in repair.