Have it in 3rd gear, then change to 4th, but keep the paddle pressed in, then floor the throttle with the paddle constantly pressed. If u don't keep paddle in, when you floor throttle, it will change down a gear by itself.
I would persevere with Revo, get in touch with Revo hq, and try and persuade them to sort it out before you start swapping tuners, might have to drive to their hq, you might be lucky and get it sorted