Fluctuating idle ... almost stalling ... almost

[dustydog]

First time I noticed this was after running hard, climbing a steep grade, hitting my 70mph topspeed on highway for a few miles, etc., I noticed the truck would almost stall and the idle would fluctuate 2-300 RPM in about 10 second intervals 4 or 5 minutes after 'run', usually when shifting into reverse (auto) and it is always a very stressful minute and things would seem to be ok. It almost seems like it may be running out of fuel? Filter is new (WIX), hard and rubber lines are near perfect. Use truck nearly every day but only put 20,000 on over the past year (usually twice that) so alot of short trips. Lift pump? What psi should it hold? Bad fuel? Refilled and ran low, drained seperator nearly no water ever. Also have bubbles that come out around injector bases on 3 cylinders but it has done that for the past 100,000 or so. Freaking out! Not ready to pull truck off road just yet but when I do I'm doing a full resto and build for power/economy, maybe add an Allison (will 545 handle it?) just can't afford that now. (VE Rotary pump & no Diesel knowhow, gas engine - OK - but diesel I'm ignorant)