Tie rods might be a culprit. Get those checked before an alignment. Make sure that all tires are wearing evenly. E150's will need to be aligned more often then the HD E250 and up versions since the suspension setup is different.
I like the Michelin LTX tires, ride very good on the E450 at work!
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1993 Dodge Spirit 2.5L TBI, 100hp
1999 Ford Taurus 2V 3.0L, 145hp
2000 Dodge Durango 360, approx. 285hp @ crank
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