Hmmmm
 

What would cause a merchant to never be able to hold formation and keep up with other merchants, despite having a 20 knot top speed list? underpowered? boost power in the .sim file?

The HEIAN MARU(Large Modern Passenger Freighter) from ship pack by miner(added as HEIAN MARU in my ship pack) has this issue. It always falls behind and out of formation. Want to fix this.

Are you looking at a speed in the CFG file, or the SIM file? The SIM file rules... The passenger ships seem to be slow to get to speed, and that may be a contributing factor. I have not seen one "keep speed" too well either. Also, the big passenger ships require what appears to be around 1200 meters of distance between themselves and their neighbors. I've not done any "scientific" testing on it, just quick and dirty tries, and with other big ships, they need a wide swath of nothingness about them, more so than a CV or BB even... Rockin Robbins has that huge convoy from hell mission, and it's the passenger ships in it that have issues with staying in formation with the others there also. So it might just be the class of vessel being a problem...

Interesting. It's actually classified as a merchant though. I'm thinking about doing some adjusting when I get a chance. Been refining my traffic for 44 and 45 and things that go along, going to release it here soon.