I'm assuming you already verified that the PTO is not engaged. Do you have to use excessive force to change gears while traveling? Is it a particular set of gears or all? I once had a twisted main shaft, on the bench everything shifted beautifully. In use , once out of the first gear selection, you fought. In the middle of the second overhaul, I placed the bare shaft on the brand new bench, it wouldn't sit still. Found shaft twisted(by accident) only a couple thousandths. Never woulda found out if not for that shiny new bench.