Shifting too far in 3rd gear....?

You have a few things to check.
One thing that can happen is the ramp or taper that the brass ring rides on can wear.
Also the brass ring can wear.
You check them with the gear out and you push the ring down and make sure it stops spinning.
If it doesn't stop turning the trans gear will never sync and line up.
I had this problem in a 3.09 gear set with second gear.
Drive it normal, no problem.
Add high RPM and it would not shift into gear.