85 F-150 questions

Just got a project truck, it's 4wd with 4spd manual, straight 6. The biggest problem I have found so far is the tranny. When I drove it home the day I got it, I had a hard time finding/shifting into 3rd. 3rd is now gone. When actually driving, it feels as if the gearbox is moving. Shifts into all gears without difficulty if the truck isn't actually moving, lol. I did get into 3rd once yesterday by double clutching, but couldn't get it to act right again. ALso had an intermittent shearing type noise after shifting into second. Checked fluid, seems fine, clutch seems to be ok but I am extremely limited with manual trans diagnostics. I am assuming at this point that the tranny is gonna need replacing, but I wanted to get other opinions on this. TIA!

hello not sure but noise possibly bearing also check the shifter & linkage to make sure its working properly.neither problem will require a new trans