I was just reading a report on Amtrak's 1974 Northwest operations. They had three trains between Seattle and Spokane that summer: The EB, North Coast Hiawatha, and the Expo '74, which only ran that summer. In August, between the three, they averaged 97% of trips arriving at the final destination within 20 minutes of schedule. At that time, Amtrak was using a mix of SDP40Fs and F3/5/7s. I doubt that they've done better than that since!
I know that, in the 1974-1978 period, the westbound Empire Builder was almost always on time at Pasco, because I routinely saw it when getting off work. I was working nights, and by leaving work a little late, I could count on meeting the train along the west side of Pasco yard.
I think part of the problem is that their newer locomotives are basically Americanized European designs. Yes, Europe has very nice passenger trains, but how many run 2,000 miles with the same locomotive, through multiple geographic and climate conditions? In my opinion, they'd do better to start with a modern freight locomotive. UP and BNSF both run stack trains at near-passenger-train speeds, so a "cosmetically enhanced" version should be able to handle a passenger train.