From Vegas to the I-70 turnoff on I-15, you are in range of the Intermountain Inertie System.
http://www.utahvhfs.org/snowlink.html I've found it to be
very impressive - the repeaters are mostly RF linked and have tremendous coverage. Once you start up into the mountains, the Colorado Connection
repeaters start to appear.
http://www.colcon.org/repeaters.html The one in Grand Junction and the one in Glenwood Springs will cover the canyon
pretty much all the way to the summit. Once there, you can start picking up the Denver area machines. The Colorado Repeater Association also has a
nice network of linked machines covering the Front Range, and quite far out onto the prairie.
http://www.w0cra.org/new/
Things get sparse in Kansas, but I've found activity in most of the larger cities along the route, particularly Topeka and Manhattan. Once you approach Kansas City,
there are tons of repeaters. Activity there is up and down. On my last trip through, last February, there was a lot of activity on several of the repeaters, but in many previous trips, I heard little to none. KC is where I turn left to go home.
The way I do these trips is to have a mobile rig with 1,000 memories that I can divide into scanning banks, and have banks of 100 set up for eachof the regions I'm passing through, and I also have the ability to change it while I'm on the road by use of a programming cable and a little netbook. I have one 100 memory bank programmed with all of the two meter repeater frequency pairs along my route, so I can scan them all if I'm in an area where I don't know where to listen. With 128 memories, you could do that too, and have 28 left over for important repeaters you know about along the route.