Hi mate, I don't think it's a problem with your trans. Everytime I first start up and drive when the engine is cold, the car will keep revving (ie. it doesn't switch to the second lobe - where the revs drop and rises again) upon acceleration. When the car's warmed up (temperature reaches halfway), the revs will then drop and it'll be normal - where if you are at a standstill and accelerate, the revs will rise then drop as it switches to the second lobe (my theory anyways). I think it's a precautionary measure to protect the trans. Mind you I never take the car over 2000 rpm until the engine is up to temp, and it might totally be unrelated since you mention it's fine after a certain distance (4km)..