tearing my hair out trying to make it work

ok im begining to get somwhere using this script from a freebie car but the problem I have is that as I slide down the hill i keep ending up tipped upsidedown is there any thing I can do to change this?

string last_wheel_direction;
string cur_wheel_direction;

default {
state_entry() {
llSetSitText("Drive";
llSitTarget(<.4,0,.4>, ZERO_ROTATION);
llSetVehicleType(VEHICLE_TYPE_CAR);
llSetCameraEyeOffset(<-5,0,3>;
llSetCameraAtOffset(<5,0,1>;
llSetVehicleFloatParam(VEHICLE_ANGULAR_DEFLECTION_EFFICIENCY, 0.20);
llSetVehicleFloatParam(VEHICLE_LINEAR_DEFLECTION_EFFICIENCY, 0.80);
llSetVehicleFloatParam(VEHICLE_ANGULAR_DEFLECTION_TIMESCALE, 0.10);
llSetVehicleFloatParam(VEHICLE_LINEAR_DEFLECTION_TIMESCALE, 0.10);
llSetVehicleFloatParam(VEHICLE_LINEAR_MOTOR_TIMESCALE, 1.0);
llSetVehicleFloatParam(VEHICLE_LINEAR_MOTOR_DECAY_TIMESCALE, 0.2);
llSetVehicleFloatParam(VEHICLE_ANGULAR_MOTOR_TIMESCALE, 0.1);
llSetVehicleFloatParam(VEHICLE_ANGULAR_MOTOR_DECAY_TIMESCALE, 0.5);
llSetVehicleVectorParam(VEHICLE_LINEAR_FRICTION_TIMESCALE, <1000.0, 2.0, 1000.0> );
llSetVehicleVectorParam(VEHICLE_ANGULAR_FRICTION_TIMESCALE, <10.0, 10.0, 1000.0> );
//llSetVehicleFloatParam(VEHICLE_VERTICAL_ATTRACTION_EFFICIENCY, 0.50);
//llSetVehicleFloatParam(VEHICLE_VERTICAL_ATTRACTION_TIMESCALE, 0.50);
}

changed(integer change) {
if (change & CHANGED_LINK) {
key agent = llAvatarOnSitTarget();
if (agent) {
if (agent != llGetOwner()) {
llSay(0, "You don't have the key.";
llSleep(.5);
llUnSit(agent);
} else {
llMessageLinked(LINK_ALL_CHILDREN , 0, "WHEEL_DRIVING", NULL_KEY);
llSleep(.4);
llSetStatus(STATUS_PHYSICS, TRUE);
llSleep(.1);
llRequestPermissions(agent, PERMISSION_TRIGGER_ANIMATION | PERMISSION_TAKE_CONTROLS);
llSetTimerEvent(0.1);

}
} else {
llSetTimerEvent(0);
llSetStatus(STATUS_PHYSICS, FALSE);
llSleep(.1);
llMessageLinked(LINK_ALL_CHILDREN , 0, "WHEEL_DEFAULT", NULL_KEY);
llSleep(.4);
llReleaseControls();
llStopSound();
llResetScript();
}
}
}

run_time_permissions(integer perm) {
if (perm) {
llTakeControls(CONTROL_FWD | CONTROL_BACK | CONTROL_DOWN | CONTROL_UP | CONTROL_RIGHT |
CONTROL_LEFT | CONTROL_ROT_RIGHT | CONTROL_ROT_LEFT, TRUE, FALSE);
}
}

control(key id, integer level, integer edge) {
integer reverse=1;
vector angular_motor;
vector vel = llGetVel();
float speed = llVecMag(vel);

if(level & CONTROL_FWD) {
cur_wheel_direction = "WHEEL_FORWARD";
llSetVehicleVectorParam(VEHICLE_LINEAR_MOTOR_DIRECTION, <25,0,0> );
reverse=1;
}

if(level & CONTROL_BACK) {
cur_wheel_direction = "WHEEL_REVERSE";
llSetVehicleVectorParam(VEHICLE_LINEAR_MOTOR_DIRECTION, <-15,0,0> );
reverse = -1;
}

if(level & (CONTROL_RIGHT|CONTROL_ROT_RIGHT)) {
cur_wheel_direction = "WHEEL_RIGHT";
angular_motor.z -= speed / 6 * reverse;
}

if(level & (CONTROL_LEFT|CONTROL_ROT_LEFT)) {
cur_wheel_direction = "WHEEL_LEFT";
angular_motor.z += speed / 6 * reverse;
}

llSetVehicleVectorParam(VEHICLE_ANGULAR_MOTOR_DIRECTION, angular_motor);

}

timer() {
if (cur_wheel_direction != last_wheel_direction) {
llMessageLinked(LINK_ALL_CHILDREN , 0, cur_wheel_direction, NULL_KEY);
last_wheel_direction = cur_wheel_direction;
}
}
}

uncomment and play with the vertical attractor settings