I am trying to use the speedometer parameter page to change the rear ratio on a '98 Firebird from 2.73 to 3.23. I get N/A for current diff. and current tire. When I put in the tire size (245/50x16) and the new gear ratio (3.23) and push the recalculate button, it tells me the new calculated values and the transmission shift point adjustment (-12.87%), but when I click on the Adjust button no shift tables are displayed. Am I doing this correctly or did I miss something ? Also if I put in the current tire size and 2.73 rear (currently in car) the calculation tells me the transmission needs 3.9% adjust. and H0101 & H0104 change. I am using the latest public release of 7.3.0 updated Nov. 22, 2005.