OK.. Why the hell are you using cheap ass servo's.. in offroad you need the best. Futaba 9451.
What version of the spectrum are you using? the original greay unit? you need a powere cap for the reciever, spectrum make one for it.
If you are close to the unit it will often feel like a super lag on the servo. when in racing or just driving conditions you will be fine.
Also, Get rid of the spectrum as its shit. should solv all your problems