Where can I improve?

I would get a new RT, since Gregg is only 249 lbs, which is very small. Weight factors into player models, so he'll get pushed around a lot regardless of his blocking stats and strength. I would sell him and buy Willie Anderson, which will give you about 200k profit.

Unless you're on current gen, sell Chris Johnson because his price is so high. His abilities (0 AP HJ, 0 AP Evasive) are more geared towards Current Gen, since field sense wasn't introduced. To replace him I would get Bettis, Sandcastle, Bo, or even CMC. At least 750k profit.

If you want, you can get Marcus Williams and sell Leon Sandcastle. Sandcastle's 80 tackling might be a problem as WRs continue to evolve. Like Sandcastle, WIlliams get Deep Out Zone KO and PA for 1 AP.

With the ~1M profit, I would get Derwin to user. He gets Mid Zone KO and PA for 1 AP, and if you want he can get Secure Tackler for 1 additional AP. If you don't want to get him, Warner gets Mid Zone KO and Lurker for 1 AP, and can get Defensive Rally for 1 more AP. If you do get Derwin, to keep the 40/40 Legends TT buy a CB5 filler like Champ, Revis, or Porter; if you don't want to spend that much on a filler, get Woodson, Johnson, or Lane.