Wow you are way down on power for that bad boy. As said MPH will tell you what kind of power the eng is making. I agree with use one timing light and set it for best power on the dyno. Honestly if the timing light is right then 42 sounds to high as most of these engines with modern aluminum heads seem to only need between 32 to about 38. To much in high gear once rolling can actually hurt power some. Many racers would actually retard the timing some in high gear once the cars weight is moving along. As said if you can get the car on a chassis dyno and tune from there it will help a lot as you are definetly missing some power that your eng should be making. As for shift rpm ??? Maybe I am just an old fool but 99% of the time I race I never even look at the tach going down the track. I just shift by how the eng is pulling by the feel of it. When it feels like its done pulling and peeking out I shift. Then I can mess with it some from there but my car is very consistent when I just shift by how the eng sounds and feels to me. And I don't think your shift point is the problem you have. Heck it could be as much as an improperly adjusted throttle cable which I am sure you have checked ? Good luck with it but get it on a chassis dyno and if you have any friends who are very good with hotrods and engines take them with you as the more heads thinking on this can be better to help find the problem. Good luck and keep us posted. Ron