Un fortunately RTF radios are always junk imo. You have to start a process of elimination from loose batt in Tx, crytals, interferance from esc....on and on.... I had probs withmy stock setup and eventually found my Rx wasnt working right. If I put pressure on the servo plugs where they went into the Rx everything worked fine then if I wiggled then or tried to fly the main motor would cut in & out.
I too eventully wound up on a Dx7....