Aftermarket kick down cables

well ive only tried adjusting it from the carb. I read on another article that the more you back it out the longer it will stay in gear (before i adjusted anything it would shift from1-2 at about 8 to 10 and 2 to 3 and about 12 to 14 and wouldnt down shift at all) Then i started slowly backing it out a 1/2 turn at a time and it would progressively get better and now its backed out all of the way and it shifts from 1-2 at about 12 and 2-3 at about 18 my speedo is a little off so im kinda guessing speed trap near my house said its about 8mph off. And now it will downshift but if i shift to second and get on it it will not downshift to first but it will from third to second. And if i get on it and hold it from first it will up shift at about 3500rpms and about 25-30mph i believe. Is there a step in the adjustment that im missing or something or is there something wrong with my tranny?