I heard from a Ford mechanic and parts supplier that they stopped producing the 4.9 straight 6 because it was too damn good and the vehicles lasted forever.
I bought the last year, a new 1993 E150 with the 4.9 and it has been incredible. It has almost 270k on it and it has been beating like a dog eyt still runs like a clock. If it weren't for the slight exhaust leak, you'd barely hear it.
Converely, a buddy of mine bought the same van a year later with the v-6 and it was a dog. No power and is definitley not a 200k mile car, let alone 300k like mine.
I think the body on my van will rust out before the engine goes to *****. It's gone thru 2 trannies and still keeps on ticking.