Again, i must reiterate. If your shifter in the cabin has FULL range of motion, yet will not push the selector into gear at the transmission, you likely have a separated cable. An easy way to tell is that when you pull back to 2nd or 4th, it will feel "mushy" and then hit the rubber stopper on the shifter arm.
Now, i'm not saying a transmission issue is outside the realm of possiblity, just that you may have a cable issue as well. If some chunk of debris wound up blocking the shift rails inside the transmission, this could have actually CAUSED a cable separation. Also, make sure and check the retaining bolt on the front of the trans, just below the shifter linkage where it goes into the transmission. If that's loose or missing it could cause shifting issues as well. It sounds like you've got the full range of motion in the cabin, but not at the transmission. Something has to give somewhere in order for this to happen, and the only place that can happen is either via a loose cable bracket, or a separated cable.