if you look up the VIN, it'll come back as an SSV. the so-called police package for the Expedition is mostly increased electrical capacity, wiring and cooling. BUT, finding a more capable alternator has been a chore. go figure. the brakes are bigger and the suspension has a higher payload, though towing didn't increase as far as I know, but it does sit higher. I was able to put 33.8" tires on it without any suspension mods, lifts, etc. and it still clears fine.
I've never been able to determine any engine mods, but mine sure runs like a ***** ape. and drinks gas to show it, too.
EDIT: mine didn't come with skid plates, and i have never been able to find any.
3rd EDIT: sorry about this - i have cognitive issues, so I type like that.
anyway, I paid 5200 for mine with only 96,000 miles on it two years ago in central texas. it was owned by a local FD since new. they took great care of it, especially the interior, so it looked showroom new.
unfortunately, the reseller was less than careful de-mil ing it, so the wiring was hosed and so were a host of vacuum controls. I think it cost me about 500 dollars to get all the windows and the AC working again. The whole experience has been an adventure, and I love it.