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?

There may be another adjustment. Look on the linkage running from the bell crank at the back of the manifold down to the bell crank on the trans. Is that rod adjustable? Some are, some aren't. If there's an adjustment there you can possibly lengthen it also.