If you got the money get a 6.0 and 80e swap, but it will set you back at least 2k to do. You will get amazing results and reliability though. If you are on a budget give Nelson Performance a call and get a custom tune first thing first. Other budget mods are a corvette servo, Ebay CAI, and Cal speed LT's. In your case maybe the best mid range mod would be to swap out your G80 and get a valuetrac and some gears to make up for those tires. I like 4.56's for tires that tall and 4.10's is the very very shortest I would go. Goodluck and have fun.