Flying autopilot vnav and lnav. Passing fl 200 / 250 or so the aircraft lowers clb rate or even levels up at times passing fl 300, and then takes a loooong time to target alt. Anything wrong or is this normal procedure ( acting economic clb ) ?Cruising at fl 340 or higher, the aircraft doesn't fly even but with an angle of 5 degrees up, whereas it doesn't happen at lower altitudes. Anything wrong ?Thanks if anyone can help me out.

Sounds normal, depending on what you mean by "loooong time". A jet like the 737 will cruise with some nose-up attitude.

Check your outside Temps. I had this problem last night and found that my REX and Vatsim Weather was conficting. My outside temps were 60+ Degrees (FL330). Shut down Rex and Shutdown FSinn Weather. Then reset FSUIPC dropped temp to -6

Sounds like you have a low airspeed set if you are at 250K and FL200. Unless you have restrictions set up in the FMC, the aircraft will lower pitch and accelerate to best rate of climb (see FMC CLMB page) after passing FL100. Climb will then continue at that speed. The automatic FMC selections are based on the "cost" factor you input in the PERF page. Above about FL270-FL290 depending on OAT, the Vnav will transition from Knots Indicated (KIAS) to a Mach speed and will continue to climb at that Mach speed as KIAS on the ASI begins to decrease. If you try to maintain a given airspeed on the ASI above that point ( you mention FL300) the climb rate will continue to decrease. The pitch of the aircraft at level flight depends on the OAT, the Mach (or KIAS) flown, the up-weight of the plane and of course the alitude selected. The lighter the plane becomes at a given altitude or the faster it flies, the lower the pitch required to maintain level flight.

ok, I'll check all the needed parameters and then experiment So far, aircraft behavior up to FL300 is perfect.

Flying autopilot vnav and lnav. Passing fl 200 / 250 or so the aircraft lowers clb rate or even levels up at times passing fl 300, and then takes a loooong time to target alt. Anything wrong or is this normal procedure ( acting economic clb ) ?Cruising at fl 340 or higher, the aircraft doesn't fly even but with an angle of 5 degrees up, whereas it doesn't happen at lower altitudes. Anything wrong ?Thanks if anyone can help me out.

The 250 knot speed at FL 200 is suspicious. Any chance you may not have fully retracted your leading edge slats and flaps during your climb out? (i.e. you are at still at Flaps 1 instead of Flaps 0).I ask, because it's an easy mistake to make, and would give exactly the symptoms you describe.

Thanks for the answer, Jim, I'm sure I retracted slats and flaps, however will verify this point. Also I had the problem with a new livery I didn't use so far, so I will also check the panel configuration. And see what happens depending on various cost indexes. Rene Ritter LFSB

Couldn't it just be 250 indicated airspeed, but actually be faster, i.e. groundspeed on ND or mach readout on speed tape?

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Check your outside Temps. I had this problem last night and found that my REX and Vatsim Weather was conficting. My outside temps were 60+ Degrees (FL330). Shut down Rex and Shutdown FSinn Weather. Then reset FSUIPC dropped temp to -6

Well worth checking this, had it myself a good few times before I started using ASE.G