I had my truck flywheel(240mm) lightened by http://www.racetep.com.

It cost $205 after shipping both ways.

Stock weight was around 25lbs. After lightening it was 16lbs. The biggest difference is below 1500rpms. There is still plenty of torque. Its just a more sensitive. Gas mileage is slightly up or unaffected. Top end I can't tell because the valve job was lousy.