Oh boy, that's not good.
Pretty sure this is a relatively common problem on this tractor. Bad part is you're going to have to split the tractor to get it fixed.
Do an internet search for "JD 3010 won't go into certain gears". There's a lot of results so read through some to find those that closely or identically match your gear issues. That should then tell you which component(s) inside the tranny that have gone bad.
Good luck!
