Agree with RURC, you've got a dodgy connection somewhere. Could be a dry solder joint that is being moved with the jolt of the landing, or a poor joint somewhere else.
If the steering is working 100% during the motor problem, it's not likely to be the Spektrum. I'd also do one thing at a time and keep trying. Check all connections - clean, dry and replug - then re-solder the motor wires - try again - then change the sensor wire... you get the picture. If nothing changes, change the receiver and then the speedo.
As it's an LRP, if you can do without it for a fortnight, send it to Horizon with your description above, and ask for a check - you never know... HTH
