It sounds to me as though either the speedo is over temperature and shutting down, or it's a Spektrum issue.
We have found (running 12th and GT10) that the Spektrum receivers are susceptible to dirt and dust. Take the receiver case apart, carefully remove the board, and brush out the c**p. Make sure you get all the dust and stuff out - I am amazed by how much was in there!! Then re-assemble and re-bind the receiver.
I've done that with both mine recently, and the occasional problem with a glitch or shutdowns has gone completely. I have also taken out my power cap with no ill effects - and it didn't stop the problems when fitted, anyway! HTH
