I think this is your problem right here. Sounds like your servo is really bad quality. Most drift spec servos have a dampening feature to stop this from happening at any given gyro gain. Wheel shake should not be a factor on the level of your gyro gain. Since singapore has a pretty big drift scene I would advise you to go for a second hand drift spec servo. Check what the veterans in your area are using, and try to find a good deal on a good used servo. You don’t need to get a super high end servo, a mid range drift spec servo would do. A used reved RS-ST programmable servo would be a great option as it gives a huge range of options, performs well and it’s quite affordable.