[BMERDOC]

I have to admit I'm at somewhat of a lose as to what changed in your truck so much during the alignment that you can feel such a big difference.

You mentioned that your steering wheel is not centered now. That tells me that they didn't lock it down when they adjusted toe so I'm kinda skeptical of the accuracy of the numbers. I do recommend that you at least change out the broken spring pack. I think you should take it upon yourself to check the tightness of your front suspension, steering and steering box. Also check the tire pressures to make sure they are correct. I would also recommend taking it to another shop for your next alignment.
I have steered clear of telling you about maxing positive caster and negative camber because you were trying to diagnose a problem and you found us on the Internet (thanx, BTW). But for the sake of the thread and your desire to have a better handling truck I would suggest that you skim through the thread and decide for yourself if you'd like to go a tad further to make it handle better. I have to go back and reread some of the stuff myself. Depending on how far you want to go a better alignment is all you may need. One of the simplest rules I have found so far is that without modifying the suspension the best thing you can do is remove all the shims (I'm not sure how big your shim stacks are) and perform the alignment to add or equalize the caster and then set toe. On a stock height truck removing all the shims still didn't move the camber negative enough to get it where it needed to be so adding shims to adjust it would only hurt things.