So, after reading (most) of the lengthy oil discussions and recommendations about high ZDDP levels, I went with Redline. Although pricey, I've used it before with great results both in autox and street cars.

Alas, my downshifting woes have persisted, mainly the 5/4 and 4/3. Perhaps internal wear. Perhaps Redline is just too slippery. Or perhaps my shifting habits simply don't agree with the gearbox.

Start of this season I switched to Castrol Actevo, 10w40 4T. It's a blend. Shifting improved. Slightly.

So, after checking the cam chain adjuster, I refilled with Super Tech 15w40 (dino). I did as a previous poster said and checked both labels. Sure enough, the Wally World brand has identical certifications as Rotella. It was only slightly cheaper, about a buck and change for the gallon size.

Didn't ride much today so too early to say if shifting has improved. I must say, as I left the Dyna muffler off, it sounds like a BEAST.

Hope this works!

If you're having issues with down shifting, most likely it's not getting the engine/transmission to agree. I can up or downshift without the clutch except for first and second.
It's all about how you use the throttle. If you're dropping a gear, gotta get the gas where there is no disagreement between the rpm of the engine and the needs of the transmission to fall into gear without grinding.
From second to third and up,I use the flat palm to slam the throttle closed and lift my toe at the same time. If I'm trying to downshift I give a quick twist just as I have taken all the acceleration or deceleration out. The gears must be unloaded. On days when everything is perfect, first to second or second to first works,but I stopped trying because I couldn't nail it every time. If you're using the clutch and trying to downshift get it in neutral and let the clutch lever out, goose the gas to get the engine to the approximate RPM the speed you are running would agree with the gear you are shifting to.

Technique, it's important.
I watched a guy actually Stomping on his shifter trying to get in first, after sitting at a light. The bike was most likely in neutral as he waited, turns green and he wants to go. The transmission is spun up, because the clutch is engaged and the gears are spinning.
Just because someone can Ride doesn't mean they understand How it works.
It's a prehistoric design. Gotta work with It, it's not goin to work with us. The transmission works Beautifully, for what it is. The bike will not be taught. We have to understand how it works and work within its limitations.
If you have ever driven a manual transmission that is not synchronized you have experienced the need to downshift but the only way to get that done quickly and without drama, then you were taught or discovered that getting it into neutral, lettin the clutch out,goosing the gas,clutching and dropping it into that lower gear is the Way.
Look up
Double Clutching.

No, it's NOT two hugs disguised as one.

Start with upshifting fourth to fifth. The RPM difference is minimal. Don't try it under forty five or more. You don't Need the torque creating any uncomfortable Jump if you don't nail it. Fifth to fourth?
Get yourself in that spot where the transmission is not loaded, just Rolling, not accelerating or decelerating, just as you step down on the shifter,give it the smallest bump on the gas.
Play with that a while. Hopefully you will find that it works without any jumping.  You know ya didn't nail it if you find yourself dragging the rear tire, squalling, down the road while the engine gains rpm..
I did not injure my bike while I worked through learning this.
Don't be afraid, but don't go getting Krazee. It's Not fun when the gear you got it in is a thousand rpm from transmission and engine rpm agreeing. I have dragged my tire quite a ways while I got good at it. You don't have to learn it without a clue.

I'm not aware of anyone who was having trouble with getting the transmission to play ball that it was the fault of the transmission. As rude and crude as the bike is, the transmission, kind of clunky,yeah, but predictable and useable, by operators who Get it.
Looking forward to hearing that you are winning!

Thanks. I appreciate that because I have seen your posts, and I know you know. Now, let's hope it is helpful.
If someone can add something that could help our friend,, please do.