Hey, just got tuned by Mellon and I'm very happy. My mods are in the signature.

My 2006 EVO IX has around 25000 miles, should I change the spark plugs? Which spark plugs do I need? Stock spark plugs? or 1 step colder? Which type?

 

search is your friend.

 

but to help...for the IX i would recommend that you get a set of OEM plugs preferably from mitsu...or sparkplugs.com
just be sure that the part number isnt the same as the one for the VIII...
NGK would be best bet if you wanted to go colder...Iridium IX is good...

 

Replace them and get the stock plugs