The two main differences between the 1/8 and your electrics are the bigger servos and the 5-cell receiver packs in the nitro. The fact that the receivers work fine in the 1/10 gas would indicate that the 5-cell power is not the problem unless your packs are weak.

That leaves servos. The higher-torque ones on your 1/8 scales draw a lot of power. In an electric the speedo is supplying the power rather than using it, so you're only powering one small-draw servo. Switch to dual big servos and you have a lot of ampdraw that the receiver might barely be able to supply, causing the failsafe to read weak signal. On our 1/8 we ditched the failsafes and went with a carb return spring instead - failsafes with high-draw servos just seem to be trouble.