E53 Diesel rail pressure

[MechManiac]

Hey guys first post here, thank you for the wealth of information you all have posted here! Anyhow, one day, i used the kickdown on my X, and "FUEL INJECT SYSTEM" appeared on my dash. It came off after a few days, but any time it comes off and I kickdown or do medium/slightly heavy acceleration, it will come back on! Technician said it was all 6 glow plugs and "4560 - Rail pressure plausibility delivery control".
Anyhow, I went with changing the glow plugs first. The message had disappeared by then, and never appeared for nearly a week of happy fast driving. Unfortunately it's on now and annoying me. NO hard start, no smoke, no noise, no loss of power.

Any suggestions?

What's a decent scan tool to use? I was looking at the Launch Tech USA creader vi or Equus Innova 3130. ....(something less than 250 USD that will read live data)

Any help would be greatly appreciated. Thank you!