Uh.

I drove semi trucks in the US for years....

You'd better either double clutch or float those gears, because if you don't, you're destroying your clutch brake, which means you'll have trouble getting it into gear from a dead stop. That applies for both upshifts and downshifts.

Ever sit next to an old truck or bus and hear them grinding gears to get into gear?

That's due to the clutch brake failing to stop the flywheel.

All semi trucks in the US use synchro-less manual transmissions.

When shifting a syncro-less transmission, YOU are the synchro.

The clutch in these trucks has 2 positions. You either just barely engage the clutch enough to break contact, or you depress it fully to engage the clutch brake and (attempt to) stop the flywheel from spinning.

If you do the second one while shifting a moving vehicle, you're causing undue wear and tear on the aforementioned clutch brake.