From experience flying a lot in these conditions - you will be caught in a downdraught (its a fact of flying in wave). This is caused by the upflowing air from the mountiain range being deflected upwards, the net affect is a few miles downwind the air descends back to its original level, then a while later the upflow commences again, but a reduced amount, descends, rises and descends. The big thing about wave is that it is smooth and powerful movements of air.
Take a mountain range - Mount Cook National Park in NZ (not only my stomping ground, but here you have a substantial Mountain range), with a 40 knot wind from 330 degrees magnetic (hits the mountains, ranging from 8000' to 12000' AMSL, at a 90 degree angle). Fly your aircraft downwind above 10500' AMSL (North West to South East) you'll get an initial altitude rise (hang on there 3000 to 4000 feet per minute in a loaded C206 is extremely easy) you'll level off nice and high (careful you could be close or even over 13000' AMSL) then you 'll have a nice smooth descent - again 3000 to 4000 fpm is easy) you'll drop back below 10,500' AMSL level off then rise again probably a bit less the further you travel downwind. Travelling downwind just accept the ups and downs especially if you're maintaining height. If you want to descend, and are confident and experienced in wave flying, then you can anticipate the "downs" and pole it forward, while turning through 90 degrees, try and maintain a line surfing the "down" to loose height - but CAREFUL too far downwind and you enter Rotor, or probably the most violent ride you'll have.
If you are trying to climb apply the opposite - in the Cook area, you'll get a few bumps from 8500' AMSL to 9500' AMSL as you climb through a rotor zone, try and climb at best rate when the VSI shows a climb, when the VSI shows the climb slowing off push forward to punch through the "down flowing air" as long as terrain clearance is suitable. Once you are through to about 9500' you'll feel like you're on an elevator, large smooth climbs are easy. If you are flying South East to North West as mentioned above (ie into wind) you'll want to take all the lift you can find, by watching the VSI, turning to parallel the track to maintain the climb (at best rate). If you get into the "Down" then push forward, build airspeed to punch through the down flowing air to get once again back in the "Up" But only do this if height loss is acceptable - any doubt about oncoming terrain, a 180 degree turn is the only option - remember turning to parallel the mountain range will mean you will still be in down flowing air, loosing more height. The up flowing air is either behind you or in front of you. Just like waves on a beach
As a side piece - in these conditions I have had a C172 at 11,000' 20Kg under MAUW, pulled the throttle closed and surfed the wave to 13,000' without engine power - good fun. Mind you, I don't know how it all works, I just use it most days of the year to fly punters around the place in nice smooth air, in comfort and safety.