A-833 - 4 speed - sticking and grinding at times

'66 Barracuda Formula S 273....Its been about 2000 miles since my A-833, 4 spd tranny was rebuilt and it still does not shift smoothly at times..."Like clock work" when I hit the 15 mile mark when I'm out cruising and shift 3rd to 4th I feel and hear metal grinding/shearing as I pass thru the 3rd into 4th. Especially at low rpm shifts (below 3500rpm). If I get on her hard 4500+ rpms she shifts like a knife thru hot butter! The higher the rpms my shifts are the better she shifts!!! Prior to the 15 mile mark the 1st to 2nd shift is sticky. I've experienced similar issues with a prior rebuilt A-833 in my car. Been told the Inland shifter are notorious for crappy shifting. Anyone else experiencing these issues with an Inland? I believe its running 90 wt. oil. Insight fellas???