I-40 Thru AZ and NM?

[surf twang]

My fiance' and I drive from San Jose, CA to Albuquerque, NM three to four times a year. We're seriously considering a 2007 H3 but we're concerned about its ability to handle the long grades through Eastern CA, Arizona and New Mexico, especially around Flagstaff. I've done a search and read through all the threads about the H3's power, or lack of, but still don't have a comfortable feeling. We usually set the cruise control on 75 and our Mercedes C240 has no problems keeping up or passing traffic. I'm not expecting sports car or Mercedes sedan performance but I don't want to be stuck behind semi's with no way to pass. Does anyone have any experience with an H3 on this route?