The DISA Valve is brand new. I replaced it and it doesn't have any leaks. Thank you :)

You have an vacuum leak! My suggestion - get a vacuum or a smoke test on the engine, I forgot the exact term but any Indy worth his/her salt will know what you are asking for - but you need to find where the leak is.
This is one of the most common issues with the E53/M54 engine especially if you have already ruled out the usual suspects. The culprit is generally the CCV (Crankcase-Ventilation-oil separator). Its a PITA DIY job but not impossible with some time and beer.
I have to attempt it soon on my Wife's X - not looking forward to it.

Get the test!

RealOEM.com * BMW E53 X5 3.0i Crankcase-Ventilation/oil separator

Here is a video of me driving the car after I just put everything back together. I also ran codes which I will update in a bit.

http://www.youtube.com/watch?v=4JAC7tRonZM

Current codes on the car -

DME -> F1/79 - Misfire, cylinder 4, misfiring with cylinder cutout (Misfire CARB_A), low fuel level signal, active during fault entry
Shadow-memory:
5A/12 - Exhaust temperature before catalyst, bank 1, signal line, short circuit to negative
5B/12 - Exhaust temperature before catalyst, bank 2, signal line, short circuit to negative
5D/12 - Exhaust temperature after catalyst, bank 2, signal line, short circuit to negative
F1/79 - Misfire, cylinder 4, misfiring with cylinder cutout (Misfire CARB_A), low fuel level signal, active during fault entry

ABS -> 61/FD - Steering angle adjustment necessary
5A/FE - Temporary system deactivation

when you put the gaskets back, did you tighten things evenly? you've got vacuum leak or air is siphoning in somewhere... the hissing sound - can you pin point the location of hiss?

Funny - we keep telling him he has a vacuum leak and he keeps doing other things. Dude get the vacuum test/smoke test and determine were your leak is - knowing is half the battle!

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I will eventually get the vauum test/smoke test. That is up to my friend really if he wants to bring it to a indy/dealer. I'm trying to do the best I can with what I know of the top of my head. As far as tighten things evenly and correctly I already did that. Thanks again for all the help everyone.

If you don't have access to a smoke machine, you might have some luck with more primitive tools. You could try an automotive stethoscope (9.99 at Autozone), possibly in combination with a vacuum pump with a gauge,($35 from Sears): Mityvac Mityvac MYMV8000 Vacuum Pump with Gauge - Tools - Mechanics & Auto Tools - Auto Body Repair Kits & Supplies

You might be able to hear a leak, and/or confirm that if the vacuum system is leaky or not.

Also, if you search the net, there are instructions floating around on how to home-build a quite inexpensive, automotive smoke machine.

It's only expensive if you like Cuban Cigars!!!

https://www.youtube.com/watch?v=zMok2y05jNE

Not what I was talking about...but pretty funny.