You may recall that the portion of the former California Zephyr between Denver and Salt Lake City continued to be operated by the Denver & Rio Grande for a number of years after Amtrak was created because that private railroad didn't want the government operated Amtrak screwing up schedules through the mountains.
I do recall that, though I didn't realize the effect on scheduling was the reason. The Zephyr was my favorite of the transcontinental trains. The last time I rode the Zephyr was on my way back East to college in 1966 - first time I had a Pullman bedroom to myself. It was a glorious trip, and once the crew found out I was a rail buff, they went out of their way for me - bringing me up to the engines, serving me wine with my meals, making sure I had my dining car seating (with window seat) at the best sight-seeing times (there is NOTHING like having fresh trout (loaded at Rifle, caught that morning) with a 1959 Johannisburger Doktor Kabinett while descending down into Denver at Sunset - or fresh Dungeness Crab heading through the Feather River Canyon). 'Twas a memorable trip. At Chicago, I changed to an NY Central train to Cincinnati. They had sold me a Pullman ticket all the way through, but the train (the James Whitcomb Riley) was all coach -- until they put the Pullman observation car on for me.
The only SP trains I ever like were the Daylights (Coast and Shasta) which we used to take to LA and to see relatives in Oregon.