Hi ME Smith, sorry to hear you are having problems with your Expy. Mine is a Generation Two and I went with a Remanufactured Engine from Promar Engines in New Jersey. They have free shipping and free core pick up even though I am in Arizona. If I read your post correctly, going through four engines is a huge problem and more than likely the driver rather than the engine. I bought a 2005 Expedition new off the show room floor and it lasted over two hundred thousand miles without any sort of a problem. I liked the car so much, I went out in search of another one just like it. Found one with a hundred thousand miles on it and decided to restore it to new condition with a new/reman engine. It cost me Three Thousand for the engine but estimated to go 250,000 miles is only a little over a penny a mile. Pretty cheap I would say if you take care of the engine with regular oil changes and drive your vehicle sanely. A little more about Promar;
The Warrantee on the Engine is three years and unlimited miles. The 5.4L 3Valve overhead Cam seems to have a Phaser problem that took Ford a number of years to fix. Promar uses only the updated phasers and here is what they say; "This engine is remanufactured with the highest quality parts available including camshafts, lifters, rocker arms, oil pump, pistons, piston rings, connecting rod bearings, main bearings, timing chains, timing gears, timing tensioners and rails, reconditioned cylinder heads and gaskets and new updated cam phasers."
I am just getting mine installed and in a few weeks, I plan on a Road Trip to see the Good Old USA (but not in a Chevrolet) and will post photos for you of my "new engine". I don't think I would go with a junk yard engine although a couple of guys here have done so with terrific results. I would be careful of most machine shops as if the part looks good (even with a couple of hundred thousand miles on it) they put back in used parts. A genuine Ford rebuild with OEM parts seems to be the safest if you can afford one at about Four Thousand. I took a lesser priced engine but they do use OEM Timing Chain Kit with new OEM phasers. Click on here but be sure to scroll all the way down the page as it will blow your mind how they rebuild these engines;
https://www.ebay.com/itm/reman-05-1...h=item442b22f844:g:t9eaaoswo0jwiuby:rk:1:pf:0
you might have to cut and paste this to your browser.