I have a f250 97 7.3 L when I give it gas I can

Diesel engines don't make vacuum, thats why they use a belt driven vac pump. If the noise you are hearing happens when the outside air temp. is below 0 celsius, then it is perfectly normal. 7.3's use an exhaust backpressure valve at the turbo instead of a waste gate to control boost, they also use this valve to help warm the engine up, the side effects are the hissing noise you here especially at the exhaust and the engine bogging down when the valve closes. Kind of annoying, just make sure you let the engine warm up before you take off.

Use a propane tourch dont light it start the truck
open the hood
slowely move the torch arround the top of the motor
as you hit the vac leak the engine will start to speed up since it is getting propane and reg fuel
the closer you get to the leak the faster the motor will go
and wala you found the broken or disconected hose