Might be worth a minute to gently lift the shifter out and make sure the shift stop plate is installed the right side up--tabs pointing upward. Pay attention to the "ski slope" feature. You'll know it when you see it. It's got to be up and to the right.
If that's all good, shine a light down and toward the rear and make sure the shift rod bushing is present and intact. That's the thing that fails most often and causes sloppy—and sometimes impossible—shifting. If it's NG you've got to put in a new one, and the only way to do that is to disconnect the shift rod at that coupler thingy, feed it forward until it passes through the loop behind the shifter, then install the bushing, grease it up and feed that rod back through. A PITA, but it's the only solution.
