Help with nv3500 4 speed tranny

[84scottsdale]

I have a custom built 84 k20 with a ls 5.3 engine and the NV 3500 5 speed tranny. It's hard to get into gear and grinds only when put into reverse I've tried a long clutch Master Cylinder because I thought the clutch wasn't pushing in far enough I currently just tried making the slave cylinder push rod longer both times I tried the gears after putting new master cylinder in and making the push rod longer it worked fine for a second and went right back to grinding I have no idea what else to try everything the the clutch is new, through out bearing clutches etc. Does anyone know what could be causing this. Any help would be appreciated. Thanks