Hi all,
I'm not sure if it matters, but I am experiencing this same issue at more than one FSDT scenery lately - especially KDFW. The big AA push carts for example will have what appears to be a single big black tire right in the middle of the vehicle but only partially visable from the side and under the cart. Then when I'm close enough to almost step out of my aircraft and touch it, the 4 wheel come back. The rest of the cart details seem crisp, but with empty wheel-wells, it's just an issue with the LOD of the wheels themselves. All other FSDT scenery parts, at multiple FSDT airports, seem to change LOD levels correctly.
This is routinely experienced at KDFW on my Win7x64/FSXsp2 rig using all the popular add-ons without any major/questionable tweaks.
If you have a moment some day, could you just double-check the LOD details of the push cart wheels for FSX and see if there isn't some underlying issue that could be tweaked? It's really strange... I'll see if I can't grab a screenie.
[Edit - a little while later - with some screenies]
The first shot is while slewing toward the push cart - you have to get really close to get the wheels to go to LOD1 detail. The second shot - just little bit closer the wheels finally display. The third shot - you back up pretty far and the wheels on the original push cart (1) still display, but then another push cart wheels (to the far right) disapear, even though it's closer.