So this may also end up in bug reports but ill explain it here and see if anyone has experienced this and hopefully found a fix.
Basically I built an M core ship with 1000 xs stabilizers on it for lift. Clocks in around 100MN.
I tossed 12 L atmos on it to get it going. And the usual hovers/brakes/adjusters just to test it. I filled 4 M fuel tanks. And put 2 tons of metal in the 8 linked containers for the first test.
It gained lift at about 50m/s very slowly. And even in the air it would say it was traveling at 700-800 kph but when I marked a target it seemed to more like .1 or .2 kph. Basically crawling across the air.
After a short while I was running out of fuel so I cut the engines and continued to drift upward/forward about 1 m/sec still showing 500 kph on the screen.
The ship can almost float down to the planet takes about 1-2 min from 1200 feet on Madison. A little faster if I hold the brake and C at the same time to prevent forward lift from the stabilizers.
I would like to find a way to get it moving forward at its expressed rate but I think the physics engine is overloading on the stabilizer math.
If I leave the seat... it falls normally as expected.