Ask HN: How to plan the optimal route for a moving van?

This might be a bit weird for HN, but I thought it posed a good hacker challenge :)

I'm moving from Phoenix, AZ to Seattle, WA next week. I'm driving my own 24' moving van (with car in-tow).

I'm trying to figure out what the optimal route is for this van. I want to minimize elevation changes, exposure to inclement weather, and overall driving pressure (e.g. narrow/fewer lanes, road curvature, etc).

There are the 3 primary routes one could take to make this trip:

1. I-5. (via Los Angeles) (http://maps.google.com/maps?f=q&source=s_q&hl=en&geocode=Fblh_gEdy-JR-SnLeaFQ7RIrhzGsG0o1-MdpjA%3BFX77WwIdaji3-CnBgh2LcQODgDEp8DhLJVAWYw%3BFcJp1gIdWVy1-ClVM-iTLBCQVDGa1URpRmUlEA&q=phoenix,+az+to+seattle,+wa&sll=40.446947,-117.246094&sspn=20.730412,46.538086&ie=UTF8&ll=40.513799,-117.202148&spn=20.710218,46.538086&t=h&z=5&saddr=phoenix,+az&daddr=39.5825903,-122.210198+to:seattle,+wa&via=1) I've done this drive at least half a dozen times (in a car). Things are fine (if boring) until Northern California and Oregon, when you really start to get into a lot of elevation changes. And in northern Oregon (Portland area), I inevitably seem to get caught in a combo of rain + chewed up highway that I don't think I'd like to navigate very much in a 24' truck with car in tow.

2. I-84. (via Salt Lake City) (http://maps.google.com/maps?f=q&source=s_q&hl=en&geocode=Fblh_gEdy-JR-SnLeaFQ7RIrhzGsG0o1-MdpjA%3BFcm_bQId53NU-Skb8Pps3_RShzG650FYs2ragw%3BFcJp1gIdWVy1-ClVM-iTLBCQVDGa1URpRmUlEA&q=phoenix,+az+to+seattle,+wa&sll=37.0625,-95.677068&sspn=43.037246,93.076172&ie=UTF8&ll=40.446947,-117.246094&spn=20.730412,46.538086&t=h&z=5&saddr=phoenix,+az&daddr=40.7469536,-111.9058178+to:seattle,+wa&via=1) I've done this drive once in a car in the opposite direction. It felt flatter than drive #1, but you'd never know it judging by the terrain the route takes you over. So maybe it was my imagination?

3. US-93 and I-84 (via Las Vegas) (http://maps.google.com/maps?f=q&source=s_q&hl=en&geocode=Fblh_gEdy-JR-SnLeaFQ7RIrhzGsG0o1-MdpjA%3BFcJp1gIdWVy1-ClVM-iTLBCQVDGa1URpRmUlEA&q=phoenix,+az+to+seattle,+wa&sll=40.513799,-117.202148&sspn=20.710218,46.538086&ie=UTF8&t=h&z=5&saddr=phoenix,+az&daddr=seattle,+wa) Never done this route before. It's the default suggested Google route.

So does anyone have any heuristics or insight into what the best route for this 24' truck would be?