There's a certain amount of momentum your mount has to build up to get to full speed.

Uneven ground with little rocks and stuff, those little wooden bridges in swamps that are 'bumpy', and the mount losing contact with the ground for any amount of time can more or less reset your speed to where you're not at full movement.

Jumping usually slows you momentarily but you can resume your pre-jump speed when you land, assuming it's smooth ground. Falling for a while and bouncing might reset you.

To achieve consistent speed, go around small obstacles or things which might cause 'bumps' and don't jump or fall if you don't have to.

The fastest way to your destination isn't a straight line -- it's the smoothest road.

I jump on to and off of all bridges.

I jump when ever i see rocks.

And, yes ride around obstacles.

And, as above, the longer road is usually faster that the cross country shortcut.

I've been wondering why my maxed out mount was so slow, even with green tree slots. I looked in the assault line and saw I hadn't even bothered to enact the passives. For months now I've thought speed was nerfed. Back at top speed is great, but I've yet to shake that feeling of idiocy at overlooking those passives. Not to mention how bad the mount felt in Cyro. I almost jammed the l3 through the controller on numerous occasions. Talk about feeling mount speed was inconsistent. I hope you found a solution. Cheers.