I've towed many times from Frisco to Colorado Springs, Pueblo, and Alamosa, CO. I take CO-91 to Leadville and then US-285 to just south of Buena Vista. Turn east on US-24 to Colorado Springs.
There is a long grade (2nd gear, take your time, enjoy the scenery, not much traffic) from Frisco to the top of Fremont Pass. From Fremont Pass on to Leadville, it's some up and down, but mostly down from the pass. From Leadville, US-285 generally follows the Arkansas River down hill to Buena Vista. US-24 has several up and downs, but not long grades and generally down hill to Woodland Park. From Woodland Park, it's a down grade (exhaust brake time) just about all the way to Colorado Springs. US-285 has more traffic than CO-91 and US-24 has much more traffic, and from Woodland Park to CS, it's lots of traffic.
I usually stay on US-285 to just west of Salida and take US-50 to Pubelo. It's generally down hill and follows the Arkansas River all the way from Leadville and less traffic than US-24. Another alternative with even less traffic, depending on where you are going, is to stay on US-285 to Alamosa before turning east. LaVeta pass is easy going east... short climb up and a long down grade on the east side to near Walsenburg.
My wife and I have been traveling (towing and hauling) CO for over 43 years and love the mountain scenery. We usually go in the late spring/early summer and fall, but avoid the tourist traffic in mid-summer (July 4th to Labor Day).
Bill