Pretty much confirms what I was thinking. That the KC Grand Prix and final arc will make up season five.
And according to TV Tome...
4Kids have today released details of the first season 3 DVD release. Due on March 8, "Back to Battle City" (Volume 3.1) will include the first four episodes of season 3 - the entire "Back to Battle City" duel and the first part of "The Darkness Returns".
In addition to the standard DVD/VHS release, an exclusive Starter Box will be available from Target stores starting April 5. The starter set includes an art box which will allow fans to store additional season-three DVDs and also includes a bonus Yu-Gi-Oh! yo-yo.
The individual DVD is priced at $14.98 while the Starter Box will set you back an extra $10.