Haha, yep. Their top speed is good but they aren't known for their speedy accel.

That would be an extremely slow acceleration. If you put this locomotive in the composition with Mark 4 coaches it rides IRL it is already the slowest train I have made so far.

Hey, I found the max accel for this loco. It's rather slow at 0.21m/s^2. Think that this can be changed? https://eversholtrail.co.uk/fleet/class-91/

is that on the old mod still? You need to update to the new locs and coaches separately. (disable the coaches mod and enable it again)
To test this theory you could try it in a new save, where it should work just fine.

Just to say the engines textures aren't loading but the separate carriages do