I have used the 5760339 code frequently. It does not give an upgrade, but it is combinable with any coupon that provides an upgrade, a free day, or dollars off. Combining this rate with Entertainment or Sam's coupons can be terrific. From Entertainment, you can use a free weekend day with this rate (2004 coupon code 10008612; 2005 coupon code 10009120) or to combine the 2 car class upgrade coupon (taking you from compact to standard) (2004 coupon code 10008613; 2005 coupon code 10009121). You do have to surrender your paper coupon at the time of rental, so don't book these if you don't have an Entertainment book.

It is my belief that Standard cars don't actually exist. I've never seen a sign in any National lot for standards. I believe that cars go from intermediate to full. If a standard is less than a full, I'd take a standard.