RE: power box problem
Please disconnect the power box and range-check the airborne system in your model with a regular 4-cell NiCd battery pack plugged into the receiver and operating several servos. That will let you know if the difficulty is in the receiver, or in the receiver/powerbox combination. It could also be in the routing of the receiver antenna and the other associated wiring. If all else fails, remove the receiver from the model and mount it on a non-metallic stand so that you can perform a good range check of the 'bare' system. If it range checks OK there, then it's OK, and you'll have to take a very hard look at how your equipment is all installed. Routing of the antenna, the servo wires, pushrod wires, power wires, and so on, can all make a significant difference in how the airborne system performs.