The waxing suggestions above may be right on. Still, another possibility is that your carving technique may contain a bit more Scarving than you realize which may deplete speed quickly without a steep slope to overcome the added friction of scarving. If so, cleaner carving will help maintain speed.
You may also be using too much edge-angle for the desired turn shape/radius.
Instead of tipping quite so much we can generally achieve the same radius by reducing edge-angle and adding Independent Leg Steering in it's place. This will produce a turn that feels more 'skidded' but the flatter ski will ride up higher on the scraped-off snow and create less friction overall because pressure is distributed over more of the base material and less intensely against the metal edges.
With regard to waxing technique, most of us wax the skis quite well down the middle of that slippery base material - but it's near the edges where slipperyness is most needed. When a ski is 'flat' our weight is distributed over the entire base and the kind of wax used there should be such that it slips well with low pressure in the target snow conditions.
When a ski is on largely edge, only the narrow section of base material next to that edge supports our weight and the pressure per square inch there is much higher than when the ski is flat. This suggests that wax near the edges should be such that it slips well under higher pressure in the target snow conditions.
Another thing to consider is that Base Prep near the edges might need to be managed differently than down the center of the base due to the greater abrasion and higher friction in that zone (due to the higher loads experienced there). For this reason the base structuring as done down the middle might not be ideal for base structuring near the edges.
Racers looking for maximum performance should probably consider all this when selecting their base prep and wax application technique.