COSTCO code also has a free driver. Rates were similar to the Wal Mart code.
Alamo (PHX) not only asked to see my COSTCO card but swiped it in order to capture my membership number.
The problem is the code wasn't really valid for years. The code hasn't been in the stores or in a public part of their website for at least 5 years. A poster in this thread found the "orphaned" page and added it to his favorites.
That said Alamo had no business making a reservation using a code that expired.