 You've Killed Your Fuel Module
Your fuel tank is located right under the middle-back of the van. When you backed over the curb you may have either made contact with the fuel tank and transmitted that impact to the fuel module, or else the "jarring" of going up and down could have transmitted enough momentum to damage the fuel module. Unfortunately the sending unit for the fuel gauge on these puppies is integrated with the fuel pump and inlet strainer, and so you must purchase the entire "module" as a unit. I just went through exactly the same problem. Here's the kicker - I'm not sure what Ford says about warrantying their factory parts, but Carter (a major manufacturer of after-market fuel system parts) has said that in order for them to honour the warranty on a module, the fuel tank has to be removed and steam cleaned. Rather than pay a mark-up from a parts house I ordered mine online through Rock Auto. Anyway, I'm willing to bet my professional reputation that that's what you'll wind up having to do (either that or use your trip odometer as your new fuel gauge, something I did for about six months until my wife forgot to reset it when she filled up and I ran out of gas in the middle of frickin' nowhere). | 
