I went on a Railway Touring Company supposedly all-steam trip to Myanmar a few years ago. Over a week, due to the state of the track the train never topped 25mph, and was often slower for hours on end; and it was pushed by a diesel the entire time, only in very light steam with 50lbs on the clock.
An absolutely catastrophic waste of time and money - the loco used wasn't even in proper working order. It was like as if they took it out of a scrap line and lit a few old newspapers in the chimney to make smoke, and pushed it along.
The schedule was nonsensically over-ambitious too - one evening we arrived at our destination at 11:30 pm, to a cold dinner of bananas and some sort of sludge - Myanmar food is by a long way the worst in Asia - despite being promised we'd be there by 6pm..... we had not eaten since 11 that morning..... often we abandoned it at some point and got a bus onwards.
Myself and others complained bitterly; never, ever again.
A diesel pushing a supposed steam train is just a cop-out. I'd rather trundle at 15mph along a branch line with two bogies behind a steam engine that was actually working, than travel in any train anywhere with a steam loco up front and a diesel pushing!