Lately my Mack is hard to get into reverse . I think the u joints on the shift rod are loose or maybe the gear box on top of the transmission is worn. Anyone ever work on this issue?

check your linkage , its loose , there is a knuckle on top of transmission that the set screw backs out on , tighten that set screw and you should be back in business

Thanks Pudg . I crawled under and up today and found the u joint is very loose, but the main culprit was a rock stuck under the back corner. I need to replace the u joint how ever. I got the stay pin loose so it won't be bad to remove , my auto parts guy said to bring it in and he can probably match up a replacement u joint.