I'm not quite sure where the lag comes in when using the radio and separate channels. Mine doesn't do it and I'm running two Hitec HS-7985MG's on my elevators. They both move at the exact same rate up or down. (real fast I might add)

P.S. I know Dave is referring to lag when using the reversing Y cable but I don't believe there is any lag when using two separate channels in the radio for this function.