I think your battery has died on your vfc or some other component on it has failed. I would check the display cable going to the system card for continuity as well as the key switch but probaly not your problem as you consistantly have a F5. If you have another truck close by swap vfc cards if the problem moves with the card u know what is bad. Fyi - there is an e-prom chip mounted in the vfc, it would need to stay with the original truck unless both proms software versions are the same, you can go into config. and check versions. also forgot to mention check the part number on both vfc's and make sure it is the same, there is an old and new style one it is on a white sticker on the inside of the vfc. when you first key on after the swap expect an F-series code as the display has to reprogram the "new" vfc.