[Ether]

Put an encoder on each side (left and right).

Average the left and right encoder counts and use that as the process variable for separate left/right closed-loop distance controllers.

Use your gyro reading to keep the vehicle driving straight. Use the gyro reading as the process variable for separate left/right closed-loop orientation controllers.

Sum the left (and right) distance and orientation controller outputs and use that sum as the command for the left (and right) wheels.