the PCM and the gauge cluster actually talk to each other via 2 wires labled, Datalink + and datalink -
thats where your speed, tach and temp come from, the fuel level sensor actually goes straight to the gauge cluster and actually moves the needle and the gauge cluster reports that to the PCM, and when it gets so low, the light comes on, the PCM knows the light comes on, but as long as it has fuel pressure it doesnt care.
when i had my 05 i didnt have a tach, and i ordered a cluster with the correct mileage programmed in and swapped it in, in about 5mins and worked fine.
the only issue is the e-brake light and the TCS were on, i never dove into fix that before i got rid of my 05. PM if you have any specific wiring questions, i have a wiring diagram book, thats the reason i know the specifics about the gauge cluster.