A couple of days ago I flew the the main fleet's A320 for about an hour. I just took off from MPTO on the active runway (offline flight) with default fuel (full I think) and default cargo.
It flew beautifully, I took it up to 25000 en route to Limon, Costa Rica and did various maneuvers. I was able to step wise push the speed to nearly 320 knots IAS and perhaps a little bit more, anyway M0.80 I remember.
Being satisfied with it I decided to take the bird on an official flight from KATL to MPTO thinking that at that speed (M0.80) I could arrive in 3:30-4:00 hours (as in real life).
I started with 27000 pounds of cargo after lowering it down. In any case the default config was a bit off balance (COG forward). I loaded some 30000 pounds of fuel.
Well, to my surprise now I am right now at 33000' and in the past 2 hours I have not been able to push it past 220 KIAS without overspeeding

At this moment it is flying on this configuration:
- Airspeed 218 KIAS 9on the PFD vertical strip)
- Winds 093 degrees /09 knots
- Heading 182
- Ground speed 331 Knots
- Autopilot ENABLED
- Autothrottle ENABLED
- AP Speed: 218 ENABLED
- Altitude 33000'
- Pitch trim 2.8-3.0 (controlled by autopilot)
- Fuel On Board (now) 17940 pounds
In other words it should be the most fuel efficient mode, auto and at high altitude.
I don't know whether starting to dump fuel or what, at this speed the sun will rise and I will have to go to work.
Any ideas what I am doing wrong?