First, order a cheap magnetic angle finder from Amazon, this one or equivilant:
Digital Angle Gauge Set Neoteck Backlit LCD Angle Gauge Inclinometer Bevel Box Magnetic Seesaw Indicator with Carrying Pouch, Mini Screwdriver, Lanyard Strip, Portable with Accuracy ±0.2° : Amazon.ca: Tools & Home Improvement
www.amazon.ca
Then put your truck on axle stands under the axle tubes, after you've done your drop mods. Put the truck in neutral, you can then rotate the driveshaft and wheels by hand. Snap the finder to the driveshaft, and flats of the universal caps when they are rotated down on the opposite side, record all the angles, work out the per-universal angle differences.
You want the pinion to be about a half degree negative (pointed slightly down) relative to the tailshaft coming out of the transmission, it is more important to correct for tailshaft/diff pinion alignment than it is to correct for individual angles.
Generally, you can use degree shims to bring the rear diff pinion within a half degree negative of the tailshaft on the trans. If the intermediate angles are greater than 3 degrees, use a spacer block or stacks of washers under the center carrier bearing to reduce the intermediate universal angles.
Once you have the general idea of what your angles are, you can order kits from JTR:
This one:
The Stealth Conversions pinion alignment shim should be installed directly to the leaf spring with a socket head cap screw. 2° 3" and 4" are available.
jagsthatrun.com
or this one:
The Stealth Conversions pinion alignment shim should be installed directly to the leaf spring with a socket head cap screw. 2° 3" and 4" are available.
jagsthatrun.com
You can also get universal generic slide in u-shaped shims in 0.5 degree increments from Summit or Jegs.
Reason for pinion being slightly negative... torque causes rotation of the differential of up to ~0.5 degrees which brings the tailshaft and diff pinion into parallel alignment which means as all the universals rotate, the driveshaft does not change overall length, which reduces wear on a few things.