About the glitching ,
Did you change out the servo and try another ? ( sounds like the servo might be bad )
If you don't have a spare , just remove the one for the rudder and put it into the throttle socket and try that .
Also , what kind of radio gear are you using ? Reason - AIRTRONICS ( and others ) do NOT like to be close . Try with the ( TX ) antenna down when close to the boat .