I have an 93 7.3 non turbo hard to start and will run as long as you keep rpm above 1000 dies at idle any ideas to

I just became an diesel owner I have a 93 f-250 7.3 non turbo idi with 150*** stock. I have had as a daily driver for past 3-4 months.I was driving home from work at an stop sign I noticed a rough idle drove on at next stop it died. Motor will start as long as you have your foot on excelirator run smooth at anything over 1000 rpm, at high idle (cold start) it runs about 30 second and dies. I have replaced fuel/water separator,fuel lines on the fuel lift pump,all return fuel lines,o-ring and injector caps on return line. Still hard to start small cloud of white smoke run at 1200 rpm for 5-6 min smooth and strong.dropped to 8-850 rpm a little rough for 5 or so minutes, then let off gas completely runs for 10-15 seconds smooth and dies ( just as if fuel was shut off.) Still getting air at valstem on the fuel/waterseporatorand will not start back without throtal about half after a few 15 sec cranks and runs as long as keep at high idle,but still getting air at fuel water separator. Love the truck pulls great and when its rite runs awesome no issues until now any advice or knowledge is great,and also noticed my od/off in shifter blinks on and off while being reved up in park or netural.any tips or people out there with issues as this or anything will help. Thanks in advanced!