1970 A833 issue jumping out of 2nd gear

Thanks everyone for your input it’s greatly appreciated! Yesterday I adjusted the shifter again giving it approximately an extra turn to turn in one half of rod engagement to the second gear position.

We just returned from from a road test. 2nd gear hard acceleration 5500 RPM shift into 3rd no issues. But my hand is obviously somewhat holding the shifter in position.

It’s a mile from the main highway to my farm up a very narrow un-even tar and chip road. So 2nd gear all the way to the house. If I rest my hand on the handle holding back No issues. Let the shifter rest in the gear position without my hand and within the first 100-200 yards of the way it will jump out.

With this info are you all inclined to go with the shifter fork or synchro hub issues?

Thanks again. Eric.