Dave,
Almost all airplanes, especially scale types, have some pitch coupling inherent in their designs. Without going deeply into the subject of CGs and stab/wing relationships, the best method to fix knife-edge coupling is mixing it out with your radio. Check your vertical uplines and downlines. If these are straight then leave your CG and thrust alone. CG changes can fix pulling or tucking in downlines, thrust can assist with uplines. Again, use your radio to mix in the elevator with rudder as it is perfectly normal. Changing other things will adversely effect flight attitudes that are far more complicated to mix back to neutral.

As it is a monoplane, your mix should be quite linear at most speeds and rudder deflections.

Mark