Bf 110C issues

[Remo]

7000m do seems to be the limit, the problem being that from 6900m to 7000m the ata takes a sudden drop from 0.95 to 0.9 and goes lower as you go over 7000m (maxed her at around 7150) ata was around 0.85.
In essence I could not get her is a stable level flight at 7000m, without elevator input, and with more that 400L petrol she don't like it up there at all.

7000m max speed .. 210-230km/h (IAS)
6900m max speed at level flight , 260km/h (IAS).
6800m max speed at level flight , 290km/h (IAS).
(CEM on full)
(Speeds was with +- 250L petrol left in tank , it takes a long long time to get her up there, and I played around with different prob settings at 7000m for a long time to come to the conclusion that she wont stay up at 7000m without a fight )