The fifth and final SUN release was issued in August 1955. Starting on September 17th Billboard listed "I Forgot To Remember To Forget" on their country charts for 34 weeks and it peaked at number 4 (Most Played By Jockeys), number 1 (Most Played In Jukeboxes) and number 1 (Best Sellers In Stores). "Mystery Train", which was inteded to be the a-side, entered the chart on December 31st, had a run of just 4 weeks and peaked at number 11 (Most Played By Jockeys). RCA Victor was lucky to take over in November 1955, just when the sales gained momentum. It is said that "Mystery Train" / "I Forgot To Remember To For Get" alone repaid the investment of the label. Even today "Mystery Train" remains a popular item and accumulates more than 26 million streams on Spotify. "I Forgot To Remember To Forget" found 3 million listeners.

The original SUN Records release didn't feature a picture sleeve. As usual the label sold the record in their universal SUN packaging.

The single cannot be found on the streaming platforms, but "Mystery Train" is included on the album "For LP Fans Only" (1959) and "I Forgot To Remember To Forget" can be heared on "A Date With Elvis" (1959).

"Mystery Train" was first recorded in 1953 by Hank "Little Junior" Parker, who had also written the song together with Sam Phillips. The lyrics are simple, the loved one departs by train and the singer hopes, she will return and stay with him. The fascinating thing is the sound. It's almost unbelievable, that the music was produced just with two guitars and a bass. Elvis' voice also sounds great, including his howling and laughing at the end of the song. RCA Victor re-released the track on the extended player "Any Way You Want Me" (1956) and the albums "For LP Fans Only" (1959) and "The Sun Sessions" (1976). Elvis also performed the song in his concerts on a regular basis, mostly as a medley with "Tiger Man". A live recording can be found on the double album "From Memphis To Vegas / From Vegas To Memphis" (1969). The studio recording was made on July 21, 1955 at SUN Records in Memphis/Tennessee.

The song was written by Stan Kesler and Charlie Feathers, who also recorded it for SUN, but the track remained unreleased at the time. "I Forgot To Remember To Forget" was a part of Elvis' stage repertoire and he had sung it several times on the radio show "The Louisiana Hayride". He finally recorded it on July 21, 1955 and added the drummer Johnny Bernero to his group. The tune was much more conventional than "Mystery Train", so the radio stations preferred "I Forgot To Remember To Forget". RCA Victor re-released the recording on the extended player "Heartbreak Hotel" (1956) and the longplayers "A Date With Elvis" (1959) and "The Sun Sessions" (1976).