I have a 2002 dodge cummins 3500 6 speed 66,000 mi .That the first sign of trouble was a fast idle (1100-1200) and up & down when stopping after a 95mi run, then 2 mi later started to give me a dead pedal for a few seconds. Did it several more times in the next few miles. After the funeral i found a parts house and bought two new fuel filters and put one in and started home.Dead pedal several times on the way back home til it wouldn't clear back up after idling for 20 minutes on road side. Never died, just gas pedal did nothing. Last 22 miles on a wrecker. I don't have a shop manual for this truck ( only the 2nd vehicle i'v owned that i didn't buy a manual for) so i thought i could find out to do on here, so far i have found i need a fuel pressure gauge and how to do the key thing , found codes 0121 , 1693 , 0500. My trouble is either #1 lift pump #2APPS #3 Fuel injection pump OR all 3 What is my next step and how little money will it cost me??? Thanks ahead of time for all the answers i hope to get. I now think i need to drive it after i get a fuel pressure gauge til it acts up and check codes again.