MIKE S. - Only time I ever have an issue with clashing gear teeth in a GD CC is when I shift into gear from a stand-still. I went as far as to weld up a "driveshaft/countershaft brake" which was something IH did on industrial versions of standard tread tractors W-A-Y back in 1941, and most semi-truck transmissions have them too. The I-4, I-6, & I-9 Internationals all had counter-shaft brakes.
But once I'm in gear, and moving, and I need to change direction, I always keep the clutch down and the transmssion in whatever gear I'm in till I come to a complete stop, then shift into the gear I want next, then ease the clutch out. As MANY people have found out, there's only so many years those forged carburized gears will withstand grinding before they won't stay engaged under load. MANY old Farmall H's have had the engaging teeth rounded off for 5th gear, road gear, which is 15-16 MPH which requires starting out in 4th, about 5 MPH and shifting on the fly, which most people just "Grind them till they fit". The engaging teeth are less than 1/4" long and after 30-40-50-60-70 years careless operators have worn them out enough they'll pop out of gear. My Super H is 59 yrs old and still holds 5th gear perfectly, has NEVER popped out of gear. But I've been the primary operator of that tractor since 1968 and have NEVER ground the gears in it. So do everything you can to avoid clashing gear teeth. It only takes a second or two longer for the gears to stop turning when you shift into gear to start moving. It's part of being a "Good Operator".