I also swapped a 2 speed for a 3 speed, changed from a 256 open end rear to a 355 with a Auburn posi unit. I installed a shift kit with the more agressive shift. I have noticed that with this combo, The car performs great when I get on it, but when Im cruising around town the trans shifts through the gears way to quick, and Im in 3rd before I know it. Im thinking of maybe changing to a more moderate shift kit app. Like a RV shift pattern. I know I will lose the tire chirps when It goes through the gears, but my driving style has changed over the years