jp747 said...could it be the board? all the things taught to you are still fine but no matter what if it's a freeride board with not so boxy rails like a slalom one then you're downwind 30% more or less than previous unless really powered up..just my opinion

Yeah I agree with jp747 that it may be the board. From your first post you seem to suggest that you used to get upwind easier.
I have a 121L board (old wizzard) with 46cm fin using 8.5 sail. You would think this would fly upwind, but unless I am really powered up I find myself having a lot of trouble and often have to slog to get upwind. Ironically my old large board (carve 131) with same set up went upwind easily. Logic says it is the board.
Surprisingly my 99L board with 5.3 or 6.2 sail goes upwind with ease. If I'm just planing I can go upwind slightly and if powered up I can get upwind with ease. Well my formula board; don't even have to try to get upwind.
Of course your trouble getting upwind could be technique but I am basing this on your decent experience windsurfing and previous ability to get upwind. Sometimes it is the tools fault.
My technique tip: may need to bear off to plane, then turn upwind and keep maximum pressure on those harness lines. Sometimes I'm hanging almost infront of the mast. Particularly good if your fin spins out easy so you don't have to overload the back foot. (weight 95kg)