Hi Pflitz, now some time ago, but OK.
Tri-X has a grain character of it own, that's at least one feature of this famous film that explains why some people LOVE Tri-x!
You don't like grain (?).
Well, I don't think that the agitaion pattern you describe is responsible of the grain you don't like unless your negatives are very contrasty; but I doubt that in view of your description above. But you seem to judge the grain from the scanning results; I think you should judge grain from a proper print!
If you don't like the Tri-x grain, try Kodak T-max 400 (or Ilford Delta 400).
If you really can see the the grain on a 8x10 print from a 6x7 fresh T-max 400 negative, developed at 20° C for 6.5 minutes in D-76 (agitate as you want!), the Print must be Very Very hard, a Very Very contrasty print, really Black and White! Print it softer and the grain disappears that's my experience!
Best wishes
/Bertil