O/D Light Flashing/ Gear Hesitation?

There are solenoids in your transmission that send fluid to different areas in the transmission to shift gears. The solenoids work in combination with each other to send the fluid. There is an A and a B solenoid and they are either on or off, and they make combinations of on and off to send fluid around the transmission to shift gears. If the Transmission Control Module (TCM) 'thinks' that one of the solenoids is stuck in either the on or off position, then it would throw the code that AAMCO told you. However, if your solenoid is going bad, that may explain your poor shifting into 2nd and 3rd gear, and could also be why the TCM threw the 'no 2nd or 4th gear' code. Take it to a reputatble mechanic and they will be able to scan the car for codes, erase them, and find out what the actual problem is. Hope this helps.