To answer a few questions here:
99gmc: if your keys are cranked just about all the way, chances are that is the max lift you will get on an OBS. Our stock keys are enough to crank to the droop stops. If you need more lift ytou need a real lift at this point, something like a 6" kit with no crank, which on mant kits is about 4". You you have a picture of the front suspension of your truck you can post (picture from the front of the truck so we can see CV angles and so on).
99yuk: axle shims are used for a few reasons, you are starting to get into the realm of needing to research U joint phasing. A quick summary is that on a standard driveshaft the angle on the upper U joint must match the lower angle, if the lower angle is different you get vibrations. So typically you should not use a shim UNLESS you have a CV shaft. In that case you need your pinion angle to match with in a degree or two the angle of the driveshaft. Trust me it gets to be a pain in the ass but my advice is no shim.
mdiacont322: do not reuse U bolts they stretch and the old bolts will come loose on you...trust me. Buy new bolts. I bought from truckspring.com in Michigan, I bought a 5/8" bolt that is grade 8 and much stronger than the shit you find in pepboys and autozone for example.