Try turning up the hop up.. If its dropping and being inconsistent, the hop up may be completely off. If this is the case, the BB can be turning randomly, causing these inconsistencies.
Also, for a more predictable, consistent flight path, use heavier BBs than 0.20s. Try 0.25s (I actually usually use 0.28s in my GBB, especially for outdoors).
I love freedom and consequently America