You need a Superlift superrunner steering system when you lift a F250 that has the D50.
FYI Its going to ride worse...if thats possible with RC's springs. I would take all back and save up for a D60 and a RS kit.
If thats not a option then get the steering kit and a alignment and you will solve the problem. Whether the springs are correct..... make that salesman show you the RC parts book and prove he gave you the right springs.
Cary