Isn't a luxury often more expensive than the small SUV (5 pass)? I would not call that an upgrade.

That said, I often reserve full size, call the location 1 or 2 days prior and tell them I want the DTS. They always have it ready for me. Of course I often only use Avis in San Luis Obispo for a short 2.5 day weekend rental... They are very, very nice there and know me.