while those rules are suggested, my dealer today said the gm engineers say its ok to run over the suggested limits as long as you vary your speed often ie don't take your first long trip and set the cruise on 75 and let her rip as that could damage the engine.
When we got our Enclave CXL awd I also noticed the break in recommendation. Let me tell you, that ride to NY on I-80 at 50-55 mph was the longest trip I can remember. OTOH, we did get +26 mpg... I figure, since I was spending ~$40K that I would "follow the rules."