The stock VR-4's are supposed to get about 16 mpg city / 24 mpg highway - I'm getting a loan on a VR-4 today :D I don't know about the SL's and base models
Premium gas of course for best performance
20 gallons, premium(not joking)
idle control valve
YES.
dodge stealth is same as 3000gt stealth rt tt is same as 3000gt vr4
YES.
YES.
YES.
a 98 or 99 Mitsubishi 3000gt vr4
Yes they are and if u want to know where to see some amazing 3000GT's go to www.cardomain.com for some tricked out 3000GT's.
Yes.
Yes, you can but will involve some cutting.