I jave a 3d foamy katana, and I've only gotten to fly it a couple times due to some "issues". When I first bought it, I had a pretty small setup on it, but it flew. On the first flight, I was not up 20 seconds when all of a sudden..everything stopped. It somehow landed ok, but I could not figure out what was wrong! I concluded it was the battery, which I replaced with a new one. That seemed to do the trick. Then, yesterday I was gonna try it again. I hand launched it, and it got right up there. I did dome rolls, hovered it, knife edge, fine. Then i was flying straight, and everything stopped, again! This landing was not nearly as pretty as the other one, and I am now fixing it.
The motor seems to be acting up a bit, when it starts to ge goin, it it drops really quick, then comes back. The motor is an e-flite 370 1080 kv, parkzone typhoon receiver, parkzone 20 amp esc, hs-55's all around, and a thunder power 1320 lipo.
Any ideas??? Please help!!!

You have got a major glitch. Begin by isolating the problem on the ground. Do some range checks, do whatever it takes to recreate the problem. Then start moving and cycling out equipment untill you find what is causing the glitch. For example, move reciever antena, move reciever as far away from engine/esc/battery as possible.