He was talking about I-70 not 70mph. You're not going to be avoiding altitude on I-70. Vail Pass and the Eisenhower Tunnel are going to put you over 11,000 ft. It's clearly the most scenic route. But if you are really serious about avoiding steep climbs, you want I-80 thru Wyoming. It's also a little more direct to MN I think. But the scenery is not as good.
I don't think the steep climbs should be any big deal, but you'll probably be down to second gear at the top. Vail Pass has a steeper climb eastbound.
The chain law rarely applies to autos in Colorado unless you are pulling a trailer.

__________________
1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13