This is what you need for the Denali http://www.tss-radio.com/sirius-conn...gm1-p-228.html and this is what you need for the F250 http://www.tss-radio.com/direct-adap...ay-p-4082.html
this one won't work for the newer 07 tahoe, one is releasing at CES in january for the 07 LAN based cars/trucks. True on the fm transmitter, it wasn't FCC legal and somebody complained about hearing howard stern on their fm and they didn't want to hear it. that's why my wifes car still has the s50 with the older stronger FM transmitter.