I have an isuzu here that cannot be shifted with the levers on the top- they just won't budge. They have the slightest amount of play in them, but the thing won't go into any gear, and I even hooked it up to the shift and select cables (tranny is out, engine is out) and can't move the shifter around much at all. What could cause this?

Assuming that the engine & transmission are separate... have you tried turning the input shaft while you work the linkage?

Yeah, I did, it didn't turn. But that doesn't matter because I fixed it

Looked through this thread and took off the linkage unit, and it turns out I was in neutral, 1st, and 5th at the same time! The 1st and 5th levers were engaged while the actual selector piece was in the neutral slot, so it wasn't moving anywhere. Now it shifts just fine into all gears. I can't believe I found the answer so quickly; this forum rocks.