[Hangtight]

Does it do it going from auto to semi, but ok from safe to semi? Other option (and more likely) is a worn trigger shuttle and cutoff lever.

 

[Hangtight]

It means taking the gearbox apart. Actually changing the parts over isn't difficult, but getting the gearbox back together can be daunting if you've never done it before. An experienced tech should get it done in under half an hour from start to finish, and the parts aren't expensive.