Sounds like either the syncronizers are not working, or you've got a Crashbox.
A Crashbox Four-Speed can be identified by the little flippy lever thing on the shifter that operates the reverse safety lock-out. It's not original to your truck, but many old farmers swapped in whatever they had handy when something broke. (Just ask my grandpa. He's got more broken transmissions hanging out at his place than anyone else I know.)
Does it go from 3rd to 2nd okay, or do you need to double-clutch on that shift too? (Don't worry about not being able to downshift into first. Most people have problems with that.)
Going up you won't need to double-clutch on either transmission, just make sure that if you have a crashbox you wait for the tranny to come around. It WILL take the shifter out of your hand if you're not careful.
