1989 Toyota Pickup Transmission

First check that no brackets are bending that are preventing the clutch from being fully pressed. If the clutch lever is going as far as it should, that just leaves worn synchros inside the transmission. They rub up against the freewheeling gears and stop them from spinning so the locking ring can slide over the teeth on the sides of those gears and lock them to the shaft. Reverse doesn't use a synchro. There, you're just sliding a gear's teeth into mesh with another gear's teeth.