I drive between Colorado Springs and Port Aransas, TX quite a bit, and I've done it every way imaginable. My opinion is that the best route from Amarillo to Colorado Springs is; Amarillo to Dumas on U.S. 287, then U.S. 87 through Clayton, NM to Raton, NM, then up I-25 to Colorado Springs. However another good route is to take U.S. 287 across the Oklahoma Panhandle to Lamar, CO, then U.S. 50 to Pueblo, and I-25 to Colorado Springs.
As far as Raton Pass goes, it's no big deal. That is the only hard pull between Amarillo and Colorado Springs and it's only a 5 mile pull up the pass. Holding back to a reasonable speed on the trip down the Colorado side is worse than the pull up to the pass.
'99 Diplomat 38A- "High Plains Drifter"
'02 Wrangler Tender