wow, very happy for the quick responses, thanks.
i'm 38 and started around 7 years ago. but started 'serious' lessons only 1/2 a year now. wasted much of the time learning by myself (which is not learning a lot

)
first of all- i'll say what I really don't like about my strokes:
yes, i feel i put 100% energy on the strokes and yet as said above, i don't feel my efforts are rewarded with enough power and speed. this goes mainly for the forehand.
second thing is that DREADFUL left arm movement. i just HAVE to fix it somehow. it looks really ugly and not productive. i really HATE the final posture behind the back. how do i fix it?
SO, in order to fix those 2 things and all other things you pointed, i'll try to summon up all your pointers:
1. RELAX and loosen up - this was said a few times, so i guess it's really important. i'll try to do it literally. not being STIFF.
any more tips to work on that and making it natural?
2. make full use of my left arm, pointing at the ball and helping with fixing the rotation for contact point. i wonder what i should to to fix the ugly final posture of the arm, and to finalize it in the 'professional way' ?
3. work on rotation of the shoulders so it will time up correctly, followed by the arm. earlier shoulder rotation, and hitting the ball more in front. but jayoub95 sais that i rotate the shoulders
too early..? different observations?
4. not to pull my elbow behind my back. still trying to understand that one more clearly.
5. Split stepping - i'm afraid i need some more info and example on that one please..
6. working on being more balanced and well committed throughout the whole stroke to the end. being aware of my head and left foot.