93 chev suburban transmission problem? Replaced the original transmission about 15-18k miles ago. Last week suburban started not down shifting when stopping at light and seems to want to start out in 2nd gear; also not wanting to shift up into overdrive. Can manually shift via level into 1st gear, get started and manually shift into 2nd or Drive. Reverse is fine. Since I can shift manually am thinking is possibly a sensor problem rather than the transmission itself. Am I right or wrong ? Any thoughts? Any help would be appreciated. Thanks in advance.