I was going to post this in response to a post about driving in Northern CA but soon realized that it had really evolved into more of a trip report. The bold should text should cover that query though.
We took our newly purchased 86 Dolphin with the 22re automatic on a 3209 mile trip from Northern NM to Portland OR and back 6/26/09 to 7/11/2009. The first leg was through Vegas, Reno, Redding, Arcata up the coast to Lincoln City, inland to Portland. The return was more direct going through Boise, Salt Lake City, etc. This was our third outing in the Dolphin. It did fine on the coast and mountain areas. The worst section was Vegas to Reno due to heat. The tranny was overheating a bit. That run involves a lot of valley crossings with mountains seperating them and thus a lot of climbs. This was where I figured out that you really have to drop the tranny into second on the hills and plan on doing 45. I don't know what the temperature was there but I'm guessing it was in excess of 110 deg. F as Redding was 109 and it struck me that the Nevada desert was hotter. I'll do it at night next time. Stayed at the Bigfoot campground just East of Willow Creek, CA and it was hot there too. The AC worked great, really dropping the temperature quickly (The heater worked great too. I did a run up to Mount Hood for a night and ran the heater in the morning).
The coast highway has a nice abundance of pull outs and passing lanes to allow faster traffic past. If I had traffic stacking up behind me I'd pull over at a convenient spot and let em pass. Good for the kharma and you get a lot of horn honking approvals. BTW- Portland drivers are very considerate of slow little campys for the most part. Ogden to Provo, UT not so much.....
We averaged 13.5 mpg for the whole trip with a high of 15.7 and a low of 11.2 mpg. My impression was that a heavy head wind hurts you more than hill climbing. Of course the old head wind/hill climb combo was the worst:0)
We saw a handful of other Toyota RVs each day (howdy if that was any of you that returned enthusiastic waves)! It seemed like most frequently we'd see them when we were trudging up a hill or vice versa. Makes me wonder if mountains don't attract toys:0)
If you're wanting to get somewhere fast you shouldn't even be considering an RV. Any RV. The big diesel rigs can go pretty fast but I question the safety factor as you have to be able to stop what ever you're pushing. It's just like the winter here in NM. We get these idiots in their SUVs or trucks that think "Hey, I can go 65 in this thing in these conditions". Sure you can. But can you stop it safely when you have to. The most commonly heard saying at a crash scene in the winter is "I don't understand what happened, I had it in four wheel drive". Sorry for the tangent.....
Believe it or not, the 22re provides plenty of horses for these little campys and is a notoriously reliable engine. If you're wanting to take lots of toys with you on your adventures (pull a lot of weight) you'll want a more robust motor/RV.