Warmed up, idling too fast

[fixkick]

if the main shaft is the box , jogs. shifting will be unpredictable.
be that bearings bad or splines in side worn out.
Clutch drag of any kind and at any RPM (foot on pedal to floor) the top cause here is bad cable. the cables do not last 25 years nor make it past 150k miles in most cases and LOVE to stick inside.
worn synchro rings or wrong lube, making them fail. do not use synthetic oil here, it will fail. in 9./10 boxes.