'91 should be an AX15.
Do you have anything weird with the clutch? Noises, spongy pedal etc? I'm wondering if maybe the clutch is hanging up and not releasing. Try slipping it out of gear without the clutch a few times by accelerating a bit then just as you let off the gas push the shifter out of gear. Now that you know you can do it try it next time it sticks in 2nd, if it doesn't slip out then its the tranny, if it does its a clutch problem.