Manual hubs shouldn't be all that much, should be able to find them used for about $25 each. Check the parts for sale section here and on Pirate, most don't reuse them when doing an SAS.
The 3.0 isn't a cheap engine to build, and you don't get a lot of bang for your buck, and if it is an auto you shouldn't even try. Any one item you upgrade the 3.0 w/wont make a lot of difference.
I started out w/a K&NFIPK, then added a Jacob's Ignition system, next went on an electric fan, then turned the K&N system into a true cold air intake system, and in '04 added headers/hi-flow cat/turbo muffler. I can't say how this would work on a stock bored motor, mine as bored .020 over after I hydro locked it on a failed river x-ing in '90. But with these mod's, my '90 weighing about 4500lbs w/o gear averages about 17 mpg(21-23 on highway), and when loaded w/an extra 500lbs of gear for camping, I can easily climb the Sierra's to 7'ft and maintain 65-70mph doing it. Over the years I probably spent about $2k building the 3.0(not including engine rebuild cost), today it would be about the same to do a 3.4 swap.
The best thing to do is make sure it is tuned up and you are running the right gears for the tires, i.e. 5-spd 4.56's for 31-32's, 4.88's for 33's, etc, and if auto you will need 4.88's for 31's and 5.29's for 33's. Then improve the intake and exhaust. I wouldn't put on a hi-flow muffler, I did that w/the headers and my mpg's dropped about 2/gl, and had dismal torque on take off. I replaced the hi-flow w/a cheap turbo muffler and my mpg'/take off torque returned. Other than that it would be better to just save -up for a 3.4 or straight 6 swap, costs would be about the same.
