Honestly I cannot remember if mine has a drain plug.. I’ll have to look later when i get home. This coming spring im gonna do wheel seals and a fluid change on her, since it hasn’t been done in 4 years.If you need advice on how to do these, let me know (PM is OK) - I just did these on my 1500HD - but as I look at your 3500 in your sig, you probably won't have any issue at all.
As for 'what I did'... besides getting it back from the alignment shop, I changed out the rear diff fluid. Probably the easiest thing I've done with the Sierra, besides checking the air filter. Thankfully, my '03 has a drain plug. And both it and the fill plug came out w/o trouble.
Took about 2.6-2.7 quarts (about 500ml left in bottle #3), and checking the level pre-drain, it was within spec (so no leaks, also 'thankfully').
I finished everything last night and its a lot better in the front end along the lines of steering play, and as well as the ride. To be completely honest, the front end feels like a Cadillac
The old arms took a beating to remove them as the truck came from upstate NY. Ask @littleblazer , the passenger side didnt want anything to do with coming out.
Ill Make a post on my build thread most likely next week on how everything is after the alignment.
Thank you for the advice and offer of help! Sorry it’s about a week late of a reply, just been caught up with schools and stuffs.