On the tunnel mod, I raised it appx 3/4". If I had it to do over i would have cut the long side on the passenger side and the top and bottom ends and simply rolled the "lid" up and patch back in the gap.
As for mileage, I get very consistent 18 around town and have had as much as 25mpg when I am "forced" to maintain posted speed limits! Also ran the GTX on the 1/4 mile last week. First run EVER in that car and I ran a 14.07. A few more runs and get my light timing down and it will be in the high 13's.
Weight is 3700 lbs exactly with 53% front and 47% rear.
Russell is great!