I had exact same fun @ 25,000 miles. FSD change didn't do squat. IP change & it ran like new.
17 & 18 have to do with the optical sensor on top of IP; 35 & 36 with the fuel solenoid that releases fuel to the injectors. I got 54 on occasion also, but couldn't tell you why.
You can try replacing the optical sensor yourself; clean the top of pump & general operating area first to avoid contamination of inside of pump. I think its a T20 for top screws & T45 or T50 for sensor piece inside pump. If you see debris inside of pump (floating in the diesel) you're probably screwed & need to do whole pump; that will have gotten into rollers, etc & pump will need rebuilding. Stanadyne dealer sells parts; look in phone book under diesel injection.
good luck.
\'95 P30 Motorhome 16,500gvwr, 26,500mi<br />New Ipump @ 25k, boost, EGT, homemade remote FSD cooler