1968 Cutlass with 8,000 miles on the 2-spd automatic rebuild from a reputable trans. Shop. Will not shift into second automatically but if I pull it down to first manually and then take to second manually it will shift everytime perfectly. It also downshifts back to first at stops signs just fine. I found that the vacuum modulator tube was sheered in half and that this surely is the cause. Replaced with new tube and same result. Is it possible I'm not getting vacuum to the modulator for another reason upstream or do I need to look elsewhere? The vacuum line feeds off of the carb.