Clutch packs are for the shudder issues. To swap from a 8.8 to 9.75, you'll have to get a new rear end. The change is fairly easy and maybe cheaper than rebuilding your current pig. Maybe find an axle at a junk yard. When you have it installed, drop the cover, check the pattern and put fresh lube in it. If the axle is just whining from the gears, not really a durability issue, more just a huge annoyance.