MZahn,
If you are a Good Sam member they have a pretty good trip planner.
http://www.goodsamclub.com/travel/freetriprouting/ I have not personally used it because, as with any of the club type planners, they figure in their preferences and overlook a lot of what you may or may not want to see or do on the route.
Our favorite is Microsoft Streets & Trips with GPS, which we have used for a number of years with great success... much more so than TomTom which led us off our planned route and sent us across Utah Hwy 12 - OVER HOGSBACK, then in California re-routed us somewhere in Merced to CA Hwy 49 thru Mariposa then to our destination of Columbia. I remember seeing a sign that stated vehicles with more than three axles were not recommended - but there was no place to turn around. Let's see... one truck = 2 axles, and one 27 ft trailer, = another two axles... hmmm... four axles. NUGGETS!!!. The next three hours - and 20 miles were, well, if you have ever seen Lucy and Desi in the Long, Long Trailer, you would have a pretty good idea. The wife spoke in tongues - at least I couldn't understand a word coming from her normally sweet lips.
Here is another site that may help -
http://www.roadtripamerica.com/index.htm
I like Nick's suggetion. It is probably the closest route matching your criteria.
The less mountain travel would be to take I-40 from Kingman, AZ to Tucumcari, NM then north on 54 to Dodge City, KS and keep going north and east from there. Its not the shortest route but stays out of the Colorado mountains.
You can see some interesting sites along this route like Acoma Pueblo, just off I-40, Old Albuquerque, NM, (maybe even Grizzly), check out Dodge City,KS, the Wizard of Oz Museum in Liberal, KS, the geographical center of the contiguous United States in Lebanon, KS, big ball of string in northern KS... Pony Express station and plane museum in NE... (I think three days have been exceeded)... Or, just have a great, safe trip to point B.