What rpm do you shift at?????

If you don't have access to a chassis dyno, on the track, you can vary your shift points on each run and compare your time slips to see where it performs the best and once you have the data on paper, it's not too hard to compare. Same goes for making changes to the car. Even something small like a timing change can make a difference in a shift point. If you do have chassis dynos in your area, go to the same one each time you go. They are a good tool but it's still not the same as 'real' time on the track.