I do not do GA flying in P3Dv5.1, but do use the default King Air I saved from v4 before it was removed for editing and checking airports for traffic as it loads faster. And have be checking the GA in TG and editing my ORBX airfields in UK regions but have noticed that when trying to compile GA plans TG hangs and will not complete, and you have to use Task Manager to shut it down and as it`s the last plans to be compiled not a big deal but needs attention if and when we get another update !!!!!!!!!!!!!!!.
If you get in touch with Just Flight's support team they can look into this for you:
tried this solution if it can help you
I have sorted it now.