SM465 wont shift?

[Orangette]

Need some help, i am at a loss.

I have been driving my '78 K20 for about 2 months now, no issues at all, I have driven plenty of standard trucks and i dont ride the clutch.

except since the other day it started acting up

If i depress the clutch at a standstill the clutch acts like it should and i can put the trans into any gear (I always start in 2nd)

But once i get moving, the truck wont let me get out of gear without rev-matching, when i depress the clutch pedal it acts as it should, just the trans wont pop out of gear without rev matching, same goes with trying to pop it into gear, i have to rev match!

The weird thing is I have zero problems getting the truck to move, it moves no problem, i can stop at the stop light with the clutch in no problem.

I have adjusted the clutch linkage and it hasnt changed it at all

Any help?