With several servos, all of different makers and long control leads, it's not really possible to determine the difficulty. If you remove the receiver from the airplane, plug in all Futaba servos and perform range checks, you should be able to determine if the receiver is at fault. A non-Futaba servo may cause some kind of feedback that is showing up as an elevator glitch. Long control leads can act as antennas and cause glitches to get into the system, and show up, in your case, on the elevator channel. Solder joints can cause problems if they're not good, dirty connectors, and of course bad equipment. You may have a bad servo or receiver. All need to be carefully checked.