25mgp is not in the formula at all by any of toyota Rv's. You're lucky to get 15 maybe going down hill. I avg 12.5 and downhill at 15. Without using brakes. I am a light weight traveler and using my rig loaded or empty it seldom will exceed what I claimed.
If you go shopping for those high mpg rigs, better believe a crook is probably selling the rig. Honest joes, wouldn't claim such a
sale of 25mpg.