My 05 F150 STX developed a similar problem after 25,000 of mostly highway miles. I am former Ford tech and Dealership Service Mgr. and the pulsation can caused by warped rotors or thickness variation or runout. Warped rotors tend to cause the steering wheel to nibble side to side braking at moderate to slow speeds while thickness variation or runout causes a mild jumpy brake pulse when brakes are lightly applied more common at lower speeds. This is not exclusive to F150's. I experienced it on two Ford company cars of mine. One was some bad at 20K it would nearly spill your coffee when the brakes were applied.

In both cases the rotors must be turned. If you have low mileage 20K or less pad replacement should not be necc. Over 20K the pads should be replaced or a least deglazed (sanded flat) when the rotors are turned. Rotors generally due not warp by themselves but there is usually another cause. I agree with others suggestions that the caliper slides must be lubricated properly. Without it it can cause the caliper to stick and heat up the rotor and warp.

For those of you under warranty you may find that your dealer OK's them under warranty while other refuse because it's maint. item. IMHO warped rotors while under warranty is NOT maint. Stand your ground and request District Manager review if they refuse.