'99 E-350 Front end problems

Hello All:
My '99 E-350 5.4L has pretty much ruined new front tires in 20,000 miles. They've worn their inside edges (though not to the point of undriveablility) far more than the outside, and they've become so cupped
that it's like driving on a cobblestone road. The rear tires are like new (all four put on at once). My '89 E-250 did the same thing, but this van only has 43k miles on it! And, it has the same vibration problem that the '89 did. Does this happen to anyone else? For the cupping, I need to check the shocks, I guess, but if they went bad in 43k miles, that would be pretty unusual. The thing tracks and handles fine, but there must be something wrong with the alignment for the tires to wear so unevenly. Any comments or suggestions appreciated.
PS- My '97 Grand Marq with 172k had its last set of tires, cheap ones from Sam's Club, last 90k! I know tires won't last that long on trucks, though.
PSS- Gotta hand it to Ford, this van got 17.5 mpg to Colorado and back, pretty good for a heavy vehicle.
CN St. Albans WV
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What we see a lot with these vans is that an owner (usually a contractor of some sort) will empty a lot of equipment out of the back so they can continue working while the van is in for service.... This can really upset the wheel alignment process since so much depends on the ride height of the front suspension... Let's not forget to add that too many alignment shops will tell a customer that caster and camber are non-adjustable on these (and that is what we call a load of BS).
Inside edge tire wear will almost certainly be the result of too much negative camber ( partly poor alignment and partly from likely being heavily loaded) and/or toe out. The cupping most likely from weak shock absorbers.
HTH.
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