Had my 97 '250 (back then superduty meant the F-450) done a couple years ago. The '250s are more prone to sag than the '350s. Might be the reverse arch they use, of maybe the TTB twists the springs more. Also added a leaf to try to keep springs from sagging again.
The diesel trucks tend to be especially prone to front spring sag, as the engine weighs a few hundred pounds more, and I don't think this was ever accounted for in the suspension design....A VERY frequent topic at: http://www.ford-diesel.com/
click on the search function and follow instructions.
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