Im looking to rebuild my rear end on a 2004 gt. Does anyone know how many hp a stock rear end can hold before it will give out

 

The real question is, "How much force can it handle."
As you probably know, You can run 1000hp if you always slip the clutch and accelerate slowly.
The stock engine is rated At 260hp.
A little more info will be helpful for a real answer.
Why are you rebuilding?
What are you planning for HP and torque?
A mildly built 2004 shouldn't need an upgrade from stock unless you are planning to race.
How are you planning on driving it?
If you are planning on beating the heck out of it, it might break no matter what you do. (Usually the clutch will burn out first).