since the time stated indicates you are using straight D-76, try diluting 1:1, meaning half D-76, half water. The times get longer (9:45 for 400 speed), but I like the results better, personally.
FWIW, I don't think there is anything terribly wrong with your grain, but the fading along the one edge doesn't look right. I tend to use 400ml with one roll, or 650ml with two in my developing can. (It says it only requires 350ml for one roll, but the math is easier for 400ml 🙂 ) I'm not sure the fade on the top edge of your negatives is from not enough developer, however. Maybe from the rinse - left-over fixer on the film?
As far as agitation, I've found that it has a much smaller effect that you'd think from people's comments. I started out doing it once every minute, then read Kodak's documents more closely and found I should be doing it every 30 secs. Since I started following Kodak's recomendation, I've not really seen any difference. Just make sure you tap the tank on the table after agitating to shake off bubbles that might form on the film.
As for fixing, I don't know what you are using for fix, but I've never found I needed over five minutes in fresh fixer. Even after several rolls, a clip test has always cleared in under two minutes for me, so I can't see any reason to fix for more than five minutes. I agitate the fixer the same as the developer, seems silly to stand there for five minutes juggling a tank if I don't need to.
I don't see a lack of detail in your scans. They look exposed properly, and the grain is "normal" IMHO. The fading and markings along the edge are not normal, however. I'd look at how you are rinsing the film, and maybe your reels. Then try another roll.
