Which is more that many people who have been driving these trucks for years can say. Knowing what keeps your vehicle right side up is a very good thing IMHO.
Moogs are good. People who complain about them being too stiff either have lousy steering pumps, or forgot to grease them, or are just whiners who are never satisfied. I also like McQuay-Norris, I call them Chuck Norris part cause of hoh strong they have've held up for me. Those are also pretty stiff to move by hand. IMHO if a ball joint requires anything less than a small deadblow hammer or a cheater pipe to make the stud move around, they are too loose and will wear out fast.
Alignment can cause poor return to center, yes. In particular, too little caster will do it. You probably altered caster and camber when you replaced the uppers, pretty normal situation actually. Take it to alignment shop for that, and while there have them look at your work to see if they can find a problem somewhere.
The pop you heard could have been the upper ball joint grease fitting breaking off and departing when axle shaft yoke got against it. Not unusual, there is very little clearance there. Some folks only put grease fittings (the right angle kind) one when they wanna grease the ball joints, when they're done and ready to drive the truck they pull fittings off again and replace them with the solid caps cause of how low they are and the space they provide for axle shaft yokes.
While holding steering wheel at full lock you're forcing the steering pump to work harder (and enter bypass mode as well), which slows engine down some. If you're hydroboosted that could affect your brake assist. Alternatively, if the vac pump is about to go, or you have a vacuum leak somewhere, same effect can be observed.
