Some Interesting Problems

Hi!
I flew from Istanbul to Amsterdam yesterday. As you know the air pressure should be fixed at STD (1013hPa, 29.92in/hg) at high altitudes. But the mine wasn't. I cruised with STD altimeter setting but my altitude indicator indicated FL380, then FL376, then FL387. It wasn't stable and I had to select altitude hold mode.
While approaching to Amsterdam, I had 80kts headwind at 5000ft. When I established on the ILS at 2000ft, I had 70kts crosswind. After a while, it reduced to 25kts in just a second, so my plane stalled of course, my IAS was about 100kts.
How can I solve these? Should I select FSRealWX weather theme on startup dialog? Can it solve the problem?

Thank you so much.
Kind regards.

Hi!
Thanks for the reply.
However, altitude indicator has to indicate correct altitude with STD setting at high altitudes like FL380. So I should be able to see correct altitude when I set STD. But I don't. I'm flying back to Istanbul right now. When I press B, it sets 1000hPa etc. When I press B, it has to set 1013hPa at high altitudes, I used ActiveSky in the past, It hasn't got any problem.

I use P3D v4.5.
I mean that, FSRealWX sets pressure like I'm at 5000ft etc.
If pressure is 1019hPa, when I set 1019, indicator shows me the correct altitude but when I climbed above TA, it gets wrong because pressure gets 1013hPa IRL. I think you know that. FSRealWX loads different pressures and wind speeds when I'm on cruise.

Sir, I can't describe my problem. I use PMDG 737 and I know TA and TRL procedures.
I should select STD setting above TA. And I do it but altitude indicator shows wrong altitude. If you want, I can take a video when I'm flying.