i had the same problem with my 05' limited. took it to our small town ford dealer. found out that anytime you rotate or get new tires you need to reprogram the tpms. he went on to explain there are 2 types of sensors in the wheel, luckily mine you can reprogram with a very strong magnet. the other one you need a special little electronic gizmo. first thing you need to do is make your truck go into reprogram mode. this is done by first turning the ignition switch to the off position then press and release the brake pedal. cycle the ignition switch from the off position to the run position 3 times, ending in the run position(do not turn the key as far as to actually start the engine, just to the run position.) press and release the brake pedal once again. turn ignition switch to the off position. turn switch from the off position to the run position 3 times ending in the run position. if you have completed the sequence correctly the horn will sound and the tpms indicator will flash . it now is in training mode. the message center will display train LF tire ( drivers side ) then you need to place the magnet on the rim right at the valve stem if horn does not sound move the magnet around the valve stem on the rim. once horn sounds message board on your dash will tell you which tire to do next, until you have completed all 4 corners, horn will sound each time. there is not a tpms transmitter in the spare. if you can't get the horn to sound with the LF tire the transmitter could be bad or you need the electronic gizmo to train your tires. the transmitter in my 05' limited is the type that actually is the valve stem assembly .the batteries are made to last 10yrs. then you need to replace the whole assembly. some types are fastened inside the rim with a metal band. hopefully this will help you out, i know what you mean by annoying when it dosn't work.........
