this is what I have on my 06 Crew Sierra. Note: It depends on what treim package you get as to what kind of seating you have. I got the SLE2; therefore, I got bucket front seats; therefore, I got the amp and sub. Not that it is really worth it, just more stuff to replace to get decent sound.
"Sound system, ETR AM/FM stereo with CD and cassette player, includes seek-and-scan, digital clock, auto-tone control, speed-compensated volume, TheftLock, Radio Data System (RDS) and 4-speakers on Regular Cab Models, and 6-speakers on Extended and Crew Cab Models (with bucket seats UB1 includes Bose speaker system, Bose amplifier and Bose subwoofer). (UB1)"
Exactly. And the LT3 has buckets.