Possibly the LP book lists them as ^fast^ boats simply because they are travelling with the flow of the River
I don't think so because in the Bhamo section they make a distinction between the "fast boat" and the IWT Ferry as it is shown in a table with separate columns for IWT Ferry and Fast Boats to Shwegu. Both the time and price are different too. The table shows the fast boat as taking 3 hours to Shwegu and the IWT Ferry as 6 Hours.
In the Katha section the current edition show a table and that there is an ITW Ferry from Katha to Shwegu and Bhamo, but in the "Express Boat" column it shows N/A for both. Maybe it has something to do with going against the current and fast/express boats cannot manage it. Just guessing though.
I guess I will have to wait and see what information I can find when I am in Myanmar. I might try calling the hotels and guest houses to see if they know.