A couple of things that haven't been mentioned (I don't think - I read most replies until people started getting rummy).
Factor in a little slush time for road construction. The midwest states can really slow you down if there is major construction, they work all summer long. And then there's Western state road construction, which, half jokingly, looks like 40 mile sections of reduced speed limits (45 in a 70), single lanes, and ten billion cones, with not a worker in sight. I kid, until you cross 2 or 3 of them, you're going to remember this post.
Second thing is...and others will probably pipe up....Cruise America RV's are like prison-grade comfortable, decontented, and the company charges for everything, including dishes and use of the generator. You will likely need the generator running going down the road, if you have people riding in the back of the RV, to run the rear AC. Realize nobody wants to sit at a tiny dinette for 10 hours straight, not even your kids, so you will need to plan LOTS of breaks.
A 25' RV will drive like a large passenger van, no worries. Just know the height, it's always good to know and put a sticky note on the dash or something. Look UP. Gas station overhangs, signs, branches, low pedestrian bridges, etc. You probably won't have any trouble, it's just a good thing to be able to reference quickly.
One last one...it sounds like you're planning to shorten your trip already. Make sure you get to park somewhere for 2-3 days to really enjoy a place and take the chance to do nothing for a while. That said, Arizona couldn't be any more uncomfortable in the dead of summer, and the Midwest (Dakotas/ Mt. Rushmore) isn't exactly cool either, but it's better than. Make sure to plan accordingly and find places with hookups so you can run the AC off shore power.