Gluck Hunter

I have a transgo stage III shift kit installed on my 99 Mustang GT. It's been on my car since 2009. Today I was driving and I (you have to shift manually) was shifting from 1-2, 2-3 like normal and then I flip my toggle switch to on (this is hard wired to the transmission to activate the overdrive) and it revs up like its slipping for about 3 seconds or so then goes into 4th (or OD). After stopping I start again (every time I stop I always turn my OD toggle switch back off) but this time when I shift from 1-2 no shift occurs. I shift to 3rd and it does a 1-3 shift. I flip my OD toggle and it shifts 3-4. I toggle a few times to make sure it shifts 3-4 no problem and it works fine. I can not hit to 2nd. Then I experiment and fine that I can hit 2nd if I have the OD toggle switch on but of course once I put it on "D" or 3rd it skips 3rd and goes to forth because the switch is on.

So I can shift to each gear but not in the correct sequence. Is there anybody who really knows racing or modded tranny's that might have a clue as to what's happening? Tomorrow I'm going to check the wiring for the toggle switch on the transmission end to make sure nothing is hanging loose or damaged.