Welcome to the forum!
Is it scraping the gear when trying to get it into reverse, or is it just hard to move the lever?
"Loud" shifting? Is it generally hard to push in to the gears and whe it goes, it makes a "clunk", or a "scrape"? If so, your clutch may not be disengaging properly. A test for this is to see if shifts quietly and easily when the engine is off. If the clutch doesn't fully disengage, you are fighting the rotating massses inside the transmission.
1965 5.0 Coupe /MAF/EFI/Astro A-5 T-5/B303 Roller Cam
Mustang Manual Transmission Specialist