G T Igofast

I've got a 1991 Chevy Silverado Manual transmission that has run with zero issues until all of the sudden I go out to start it and physically cant turn the key far enough to actually crank the engine.

The ignition switch/tumbler should all be fine as i can turn the key into accessory mode, get radio, lights, unlocked steering wheel etc. but past that i get about 1/4" turn before it becomes un-turnable.

I don't believe this to be a problem with the ignition switch or the key (i tried 2 separate ones) as the problem is happening after all the important unlocking in the cylinder has happened.

Any help would be greatly appreciated as i don't want to throw money at the problem without knowing whats going on.

Thanks!