The Mitsubishi/Chrysler 3.0L V6 is famous for valve train problems. Here's a link to the factory rebuild manual:

www.twingles.com/manualcd/dsmgift/6g72.pdf

Here's a DIY guide for the job:

http://www.allpar.com/mopar/3fix.html

and another:

http://www.allpar.com/eek/ValveSeals.html

Lastly, if you'd like to buy replacement rebuilt heads from a competent rebuilder at a reasonable price, here's a link to a rebuilder that many offroaders who own Dodge Raiders and Mitsu Monteros have found to be their choice:

http://www.cylinder-heads.com/automotive-cylinder-head-rebuilding.html

Good luck!
Frank