Recentyl my 3.0 98 was having intermittent power loss, then self-fixing. I first changed the frame fuel filter. WIth the old one in hand, could not blow through it in the direction the fuel flows. New one half-ass fixed it, but was still suffering the power loss, just less frequently.
Then I read an article on the MAF. Said if you pull the plug off it while idling at operational temp, the engine should quit. If it doesn't, it's not working. Pulled the MAF off, inspected the wires. Downwind side very cleanand shiny. Upwind, or incoming air side, brown and dirty. MAF spray wouldn't remove it. Cleaned them, very carefully with a q-tip and isopropyl alcohol. FIXED. No more power loss.
I don't know what it was. Not oil, I use a stainless steel mesh cone filter. But something brown and kind of sticky. Weird. In any event, sure is running great again.