Are you sure it is in the trans and not a valve or something else ??
to get to the front pack (clutch pack) it has to be split between the engine and clutch housing.
To get to the rear pack (brake pack) you have to split and get the front pack out, be sure to get the 2 bolts up inside behind the clutch pack, then bolt the clutch housing back to the engine and then split between the clutch and transmission housing. The rockshaft housing will have to come off. take the quill off just in front of the differential and pull the shaft out to the rear. then unbolt and pick the brake pack up out of the trans case.
Easier with the cab off out of the way also
Tough job if you dont have the right tools, but not real bad if you have the right ones.
hope this helps, if not reply for more info.