To improve the efficiency of differential mobile robots (DWMR), improving their trajectory tracking capabilities is important. Especially in navigation problems with complex paths. This paper presents a new combination of Backstepping Controller (BSC) and Fractional Order Proportional-IntegralDerivative (FOPID) controller for DWMR. The improved Grey Wolf Optimization (GWO) strategy combines GWO with the Slime Molding Algorithm (SMA) to determine the parameters of FOPID. The designed controller addresses the nonlinearities, ensuring system stability and accurate trajectory tracking. The cost function used for the optimization process is a combination of Integral Absolute Error (IAE) and Integral Mean Square Error (ISE) to minimize the state deviation and enhance the response capability. The results are demonstrated through simulations on MATLAB-Simulink with different trajectory scenarios and compared with state-of-the-art optimization techniques such as PSO or GWO. The results show that the controller helps to improve the trajectory tracking ability, the cost function and the position error are improved compared to other optimization techniques.