Really cool development you have going on here! The initial melody is epic yet stately. I love the minute variations. I don't know that you need to come up with a completely new melody per se. Something melodic should happen at 2:26. It would be super cool if you could come up with a countermelody to the main theme...something that would play off the rhythms and intertwine with the notes harmonically. Present this new melody without the first theme over the horn stabs and rhythmic part, then when the key change happens later, bring the original melody back and play them both at the same time. It'll wrap everything up in a nice and tidy package, and then the new melodic material won't seem so random. Leave the completely new theme for the second movement ;)
I like the story this piece tells. Did you have a specific scene in your head when you wrote it?