I am extremely limited on my mechanical knowledge so I will start by saying that!

2003 Chevy Silverado 2500HD, Diesel.

About 3 miles from home it started driving rough and check engine light came on. Got 3 errors

P0700
U2106
P0404

Not worried about the last code (EGR, have replaced it and it still intermittently comes and goes). Worried about the other 2.

Is there any diagnostics I can do at home before needing to take this to the shop? I can do little stuff like testing fuses, but can't disassemble something major.

Just spent 3k on this thing for power steering problems. Really trying to avoid the shop if at all possible.

Thanks!