First off in lighter vein: I hope you have an oxygen system in the Bonanza as it is typically dicey for a large percentage of the population to go above 12,000ft as hypoxia becomes a concern! 
But more seriously: I believe it is generally understood that the base G36 as modelled is underpowered. The community project G36 is supposed to be much closer to the POH performance: this is what I have been flying almost from the beginning. To check the performance of this mod I just did a flight starting in the air at around 7,000 ft. (spawned in the air near a high-ish altitude airport). Set the altitude at 25,000ft. (!), engaged the AP with FLC at 100kts IAS. Set the power @ full throttle, auto mixture and prop fully fine @ 2,700RPM as required by the POH.
And it soon became clear that they improved the community mod performance a bit TOO much! Admittedly I was light (2 people on board, less than half tanks), but still…
Rates of climb at different altitudes:
12,000ft: 800FPM
15,000ft.: 550FPM
18,000ft.: 350FPM
Even at 20,000 ft. it was still climbing at a VERY healthy (and very unrealistic!) 200FPM. By this time the 100kts IAS was equating to 135kts TAS with an OAT of -24°C. For reference: the POH gives the following climb performance:
One other comment:
As a general comment: I find that the Bonanza’s AP is pretty good. A common issue is that people often tell it to do something the aircraft is not capable of and thus forces the AP to do something bad. In this case one should be sure that you are using FLC mode with the speed set at 100kts for best climb performance. With this setting you won’t get unrealistic AOA, the aircraft will just stop climbing once it hits its ceiling.
Hope this is of some use.