the SCT XCAL2 can adjust your shift points to very firm. do a search-there is a thread with pics and diagrams around here. the XCAL 2 will also correct your speedo for the new gears. it is not like the older models where you just change the speedo gear, it is electric. i have not heard of anyone running a converter in the new stangs yet. i assume by high speed that you are talking about a higher rpm stall? gears and a tune are the best bang for the buck as far as 1/4 mile performance. 4.30s might be a little steep for the auto, dependinig on what your goal is for it. you are definately going to need some suspension mods to control the wheel hop you will be getting with your combo.