Clutch won’t engage?! but it’ll push start

Got in this morning, clutch has pressure and will turn on, but won’t go into gear ??? Drive way is on a little hill, so I pushed it a bit and it’ll slide right into gear. But if truck is stationary it feels like the gears are locked. Can’t wait to see what you guys got

 

Did you try putting it in reverse first?

Edit: to better explain I mean after starting the engine if the transmission did not want to go into first gear try putting it into reverse before that then try put it in the first gear. I have found that when transmissions start to wear over time especially with the second gen pickup the synchros are very similar so if you can put it into reverse and then put it in the first gear afterwards it might be an indicator that you're starting to lose a synchro.