Don't take off in GPS, use atti or manual. I often get some TB in the beginning of a flight, close to the ground, after flying for a while I find GPS holds much better, this is true on all 3 of my MRs with GPS. Just be ready to correct for wind drift as you take off and make test flights in a very open area until you have your technique and hardware working well. If I have to work in a very tight spot, under low trees with very little room to maneuver, I first test my MR in an open space that day. And in tight spots I never use GPS.
And make sure the CG is in the middle of the MR, this is easy to test, just get the balance perfect by moving the battery, test by balancing opposite arms on your finger tips. It does not have to be perfect but get close.
Also make sure all your ESC's and motors are in perfect shape and all connections are good. Use an IR thermometer to check temps of units after you land they should all be within a few degrees, if one or two are hotter, you are either out of CG balance or there is another problem.
