It is a rubber/plastic piece that sits inside the metal part that shifts the gears, (name of metal part?) Stick your fingers in there and see if it's actually sitting in there or not. Move your fingers all around that metal part and see if you feel anything else, i didn't even realise it was in there until i felt it move, then i had to get some hooks in there to pull it out. If you find it there are two ways to put it back in, make sure the bigger side is facing up. Also keep in mind if the spring was broken at all it could be a piece of the spring blocking your path. And on another note, from what i have read, when you do a lift you have to bend or add to the shifter to make it fit better, that could be your problem too. Hope this helps.
Robert