If your 65 has the original Muncie transmission (4 bolt side cover) it is not syncro in first gear. Chevy offered a full syncro overdrive trans in 66, but the regular one was non syncro. To the best of my knowledge the full syncro 3 speed (Saginaw) was not introduced until late 67. It is common to install one of the later transmissions in these trucks and you may have one. They are much larger and have 7 bolts on the side cover.
Fred
