You only need to change the output shaft. Unfortunately to get to it you have to tear down the entire transmission. Might as well replace the consumables inside.
The 4x4 Output Shaft Assembly is part # 24204291 and can be had brand new for about $125.
If this trans is from a Motorhome, it may very well be the HD version. The HD version of the 4L80-E is identifyable internally by straight-cut gears in both rear planetary sets and externally by a 2WD tailshaft housing that has a flange on the output side with a ball-bearing (instead of bushing) for the yoke.
If you have the HD version be glad, they're hard to find and the straight-cut gears reduce wear on the thrust washers at only the expense of a little gear whine. Better power-handling and longevity.
__________________ "James B."
1998 C2500 Suburban LT: GM Crate 502/Brodix Heads/234-244cam/4L80-E/3400 TC/Gear Vendors/4.56:1 Eaton/Dual 3" and Ceramic Headers 1999 C1500 Tahoe LT