LB7 bad FPR?

Have a 2003 LB7 with 175,000 miles on it. Replaced the injectors and filters about 2700 miles ago and it was running fine till this afternoon..... Started it up and it was running rough and noisy. Shut it off and started it again after a minute; was rough for a second and then smoothed out. Drove about 50 miles and stopped for about two minutes and on restarting it was rough and noisy again and SES light came on. Drove a few blocks and it didn't improve so i shut it off and restarted it and it finally smoothed out.

On arriving home i checked the codes and it has P0088 (fuel rail pressure too high), P0089 (fuel pressure regulator performance), and P0101 (MAF sensor). P0404 is also set but i've had an issue with that for some time... The manual indicates for P0088 that with this code a fuel knock indicates the pressure really is too high and is likely a sticking FRPR.

Anyone have any insight? Approx cost of FRPR and ease of changing it?

I do have a Banks Otto Mind tuner on the truck which I leave on setting 4. Do tuners cause premature fuel system issues? Since i've had the truck (95,000 miles) I've used fuel additive and currently use Opti-Lube.

Thanks for any comments.