The "going through the gears" still applies, but in order to really "pump" both the sail and fin, you really
cannot be hooked in.
So, when you think you are fully into 2nd gear, and have moved back on the board progressively as the board speed increases, then try some big "give it all you've got" pumping of the rig. Unless you are really young and fit, you probably cannot put the level of effort required, into more than 3-5 pump cycles.
If that gets you going and pops your board up onto a plane, then go for the front footstrap, and get hooked in. Then pump the fin a bit with your back foot (not necessarily in the rear footstrap yet) to free the board up a little more and gain that little bit of speed required for the board to really "take off".
When you are sailing in marginal conditions, you have to head upwind very cautiously.
Go a little too high, and you get to start over.... yeah, the whole moving back, pumping, footstrap, hook in
gain speed process.
So, if you even think you feel the board start to slow down, immediately head off the wind a little and slightly unsheet your sail to give it max power.
Oversheeting will shut off the sails power faster than anything, at the same time reducing your boardspeed very quickly.
So, you can plane along very nicely, on a beam reach or a little higher, and maybe head up some more to take advantage of the acceleration of the apparent wind, but you must really be sensitive to lulls and having the wind get around in front of you.
Hope this helps,