Hi friends,
My friend has a GS Racing 1/8 nitro buggy fitted with a Power HD Metal Gear Servo HD-1201MG http://www.hobbyking.com/hobbyking/store/__9618__Power_HD_Metal_Gear_Servo_60g_12_2kg_16sec.html
for both throttle and steering.
Tx is turnigy GTX3.
It is powered by  4 NiMh AA Sony 2500mAh batteries.
When both throttle and steering is used simultaneously the servos jitter and the current draw is very high so that the volatge of the battery goes below 4.0V , when the controls are released the voltage regains to 5.2V

Please help us
Are the servos chosen are high ??

replace with digital servos.... you will get better control.... and moreover that servo is too much torque for throttle...
12.2kg is great for steering but too much for throttle .... use a fast digital servo for throttle.... since both servo's draw high current your battery will also run out fast.... so go for a digital high torque servo for steering and fast one for throttle .... its the best setup i found in all my cars

there is no issues with using 12 kg servos in throttle, you just have to adjust linkages and/or from the radio setup EPA so that there is no stress anywhere , im using 20kg in my buggy throttle.

i would suggest to upgrade to a better rx pack like 6.0v nimh pack first

Pravesh , I have tried 6.0V pack but the betteries drain out too soon.
When measured with a multimeter the current draw was upto 3A.
Please help me..

theres a lot of things that can be a problem. is the car running well without problems while using 5cells nimh pack? even if for little time, is it running, without the mentioned symptoms?
current draw is ok i think though on the higher side. 

Yes the car runs ok with a 5 cell pack...
But the cells drain out within 10 mins.

normally all RC nitro cars use a 4 cell pack isn't it ??

they run best with 5 cell 6v packs and 7.2v lipos too  . nobody recommends 4.8v anymore. as even servos are produced to work at 6v better.

get nimh 1600 mah rx pack and dont use pencil cells, pretty useless.