All is being said about installing a Nav system into a non Bose/Luxman truck (RPO UQA). The reality is that the Nav radio head does not need the RPO UQA or any additional amplifier system. RPO UQA just adds an amp and subwoofer system to the vehicle for surround sound (required 5.1 for the X4 Radio/DVD). The Nav head (I believe is RPO U3U) is built to work with the UQA option AND two other level radio uplevel options RPO UQ3 and RPO UQ5. The only difference is that the RADIO has to be programmed as one of these options as well as the BCM. If then radio is programmed (as most) for the UQA option, the output is only from the pre-amp and is not meant to drive the speakers without an amp. If the radio is programmed with UQ3 or UQ5, it will use its U2K which is the DRR (Digital Radio Receiver) which comes with theUE1 (GPS Antenna) amplifier and output enough sound to blow you out of the Cab! What is needed to program the radio is surely available from GM. I have seen 2008's with the Nav head w/o Bose. It is also shown in the factory service manuals with the DTC diagnostics and fix, along with the wiring diagram. So if you have RPO UQ3 (Ext Cab) or RPO UQ5 uplevel radios, you can install the Nav head, but still need the programming performed by a extremely savvy tech. If you want the fact, go to your dealer and ask to see the service manual. It is in Book 1 of the 4 Book set. Uplevel radios are the AM/FM/RDS/XM/SingleCD with the DRR (UQ3 and UE1) radios. Herein lies the problem. The service manual shows 4 radio heads. They are shown as X1, X2, X3, and the Bose is just not an amplifier, it is also a crossover/decoder system for 5.1 surround, depending on which nav head is in the vehicle, X3 or X4. X3 should be RPO U3U, NO RSE OPTIONS (DVD, ETC). The X1 connector is 14 Pin, basic AM/FM. the X2 (XM,RDS,SingleCD,AM/FM) shows no RPO code. It is based on the SLT options and whether or not you have the 6 CD option), X2, X3, X4 connectors are 16 Pin. Radio X2 is used in conjunction with the UK2 in both Y91 (with or without Y91), X3 is U42 which provides the DVD option, and X4 is U3U/UVB (without DVD). So, all being said, there are actually 2 Nav heads, one is the U3u, and one is the U42. Both have different part numbers. UQA is needed or U42 to provide the surround sound. Finding out the part numbers is going to need the dealer, as the GM Service manual provides NO gm Part Numbers which is ludicrous after you spend the bucks to purchase it. So those with the UE1, UQ3 RPO's should use the U3U/UVB (X4) radio. This has the VSS inputs in the harness at pin 5 (D-GN/WH wires, circuit 817). Denso manufactures these radios, and there are factory OEM's that can be bought that are re-conditioned. I am exploring this matter further. I have also been advised that the NAV has the ability to "bench program". I am told that when this is done, you have the option to select the UQA, UQ3, and UQ5 integration options as well as the unlock code programming. For those with LOCKED radios, here is the reason. If you purchase a radio that is not new, or reconditioned, it has already been benched and the lock code installed. The lock code is THE LAST SIX NUMBERS OF THE ORIGINAL VIN. This is how the theft deterrent system works with the communications system. All major modules have the VIN code input to unlock them. If the VIN does not match..you get LOCKED. To unlock, the radio needs to be re-programmed to contain the last six digits of YOUR VIN. You may need the original VIN of the vehicle this system was in to access the system to clear it and re-program. Be sure to get these numbers from the seller of the used head, if not, you are in deep do-do. A savvy tech CAN bench this radios, and there is a special diagnostic tool other than the Tech-2 for this. Also needed is the XM module, which I find no mention of in the Service Manuals. I believe internal to the DRR. See this link for some more useful info:

http://www.justanswer.com/questions/28b9v-2008-silverado-4x4-ext-cab

Of course, these are my own interpretations...the lock problem is actual fact, the rest is derivatives of what I have seen and explored through the GM service manuals and the above hyperlink, along with a lot of web time.