I have a 93 chevy ex-cab 4x4 5.0L that will shift up to third but not back down. It has a 700re tranny. I spent big $ on computer change and wiring search. Problem goes away and then comes back. After last garage time everything worked perfect for short time and ghost comes back. It will not shift to 4th (O/D) at all. I can manually shift up from 2nd to 3rd which means I have to start out in 2nd. Starting to really suck. Anyone have any ideas?