I agree with using a different pushrod material. Altavillan has you covered. Check out the Sullivan graphite pushrods from Tower.

These are 2-56 size. They work great. Nothing more is needed for a simple throttle pushrod. No load here. Very flexible, but stiff enough to do the job. Run your pushrod as straight as possible and make gentle curves. Use a piece of balsa or lite-ply as a brace every 6" or so.
http://www3.towerhobbies.com/cgi-bin...&I=LXFV43&P=SM

Here is the 4-40 size in case you want a little heavier. Keep in mind, it's not necessary unless you simply cannot get a 2-56 link on the carb throttle arm. The 4-40 isn't as flexible. Still recommend making gentle curves and a couple braces along the way. Keeps it from flexing.
http://www3.towerhobbies.com/cgi-bin...&I=LXFV45&P=SM

I think you accidentally installed an antenna by using the metal cable. It's a direct antenna to carry RF back to the throttle servo. Once you get feedback or interference in the throttle servo--it can travel back through the servo lead and interfere with the rest of the RX system.

10" may be just fine. I usually try and get 12", but I understand that it's just not possible all the time.

I think the graphite pushrod will solve your issues.