I'm going to say the lift pump is weak since you're still having problems, I wonder if the SVO put a little too much strain on it or something. Doesn't sound like it's sucking air to me, sounds like fuel starvation though. And yes, put the strainer in the tank!

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1985 300D Turbo ~225k
2000 F350 (Powerstroke) 4X4, SWB, CC, SRW, 6spd ~148k
1999 International 4900, DT466e (250hp/660 ft/lbs), Allison MD3060 ~73k