did you check the spacing and shim the bearings on the input shaft? https://www.honda-acura.net/forums/d...ml#post3763558
it sounds like there may be too much play. it could also be a rounded syncro but that's really not that common and you probably would have spotted it. also does it do this while driving? or have you tried driving yet?
when my bearings went out my car would pop out of second when I was making a turn it was odd but it was the bearings.