Having been on the UP Steam Crew, I believe that you are woefully misinformed as to the reasons for the diesels.
First off, the Steam Locomotive is more than capable of hauling the train. The Diesel is usually tagging along in notch 1 or idle. The main reason that the Diesel is there is to lessen wear and tear on the Passenger fleet.
How so, you may ask? Easy... A Steam Locomotive has no dynamic brakes. So downhill the equipment's brakes are what are being relied on to slow the train. I hate to put it this way, but getting Disc Brakes and installing them on old GSC (General Steel Castings) trucks is a very expensive and time consuming process. They are like disc brakes on a car, they are not easily available or replaceable like freight car brakes. Being a specialty item, are expensive to replace. Having a diesel along for the dynamic brakes just insures that the passenger equipment will be around for many years longer than they otherwise would be.
The 844 and 3985 have been through some very thorough and EXPENSIVE rebuildings in the past couple of years and are in no way any less (and are probably more) like the locomotives that they were built to be. Steve tells me that the 844 rides entirely differently and is much more powerful after its rebuild. It was no slouch before the rebuild, I remember hauling a Special Train outside of Boise at almost 100 mph (according to the tattle-tale hot box detector).
Just because the 844 or 3985 is hauling along a diesel doesn't mean that the diesel is working or that the Steam Locomotive isn't. If you don't like it, they you are perfectly welcome to not go and look and complain.
Rick Steele