exerda

The buckets are the same.

Not sure what you mean by "upgrade codes." There are discount business/first fare classes which sometimes agents mistake as being economy fares with a "free upgrade." You can find the ones which are offered via a fare search for business or first; the site unless you ask for a specific fare class will return the cheapest premium cabin fares available, e.g. an A or P fare if offered.

As a Gold, an instrument upgrade (using miles + copay) is possible, of course. We need specifics on route and date to give a better idea on the chances. You may find that a paid upgrade / upgrade for cash is a better deal in some cases, though, and is often available as the fare difference from the economy fare to the discount premium cabin fare (there are threads on the complexities thereof; I don't have one handy, but we had a great analysis posted earlier this year on the premium cabin fares in various markets).