SM465 trans questions?

[GMC Truck]

My 84 3/4 ton 4x4 4 speed has some issues and i'm looking for help. This trans was rebuilt a little over a year ago with all new brgs. and syncros. Lately I have noticed that when shifting from "low" to "1st" it wont go. It just grinds. When downshifting from "2nd" to "1st" is wont go unless the truck is not rolling. Up shifting and downshifting seems to be problematic at the same gear. I dont use "low" often but if your in low pulling a grade and try to shift to "1st" it will not go untill you stop moving. Could the tapered area where the synco rides be worn out? Aint the syncro suppost to kinda "brake" the shafts to make the next engagment possible.

 

[fouronereason]

Mine wont shift into granny gear unless I'm nearly stop and it'll grind a lil, I figured it was the low gearing and lack of syncro, Dunno

 

[GMC Truck]

I know that it wont shift into "granny" with it rolling that gear is not sycronized for that use. My trans wont go from "granny to "1st" without grinding or from "2nd" back to "1st" without grinding.