Adjusting the valves isn't too tricky. I just did it for the first time ever following 2mbb's instructions (
http://forum.ih8mud.com/60-series-wa...ml#post4300965). I did it cold, and only a few valves needed slight adjustments, but the truck ran noticeably better afterwards. It certainly can't be any tougher than removing the manifolds.
And as for replacing the vacuum lines: this seems to be everyone's first steps. These are old trucks, so what hasn't been screwed up by previous owners/mechanics is likely deteriorating. It'll run you about $50 to replace all the vacuum hoses w/ new silicone ones, but when you've done that you'll be standing on much firmer footing for chasing down the other gremlins.