PI Controller Tuning Issue

The above system is cruise control, one in which the road slope angle is taken account of and is between - [20,-20], we are also assuming the small angle approx. vehicle mass is set to 1 kg in order to first tune the system and then scale upward and the Vr variable is 1 which is the target velocity.

It seems that the road test angle is interfering with the pid controller. Therefore i cannot tune the pid controller using the auto tune function as the road test angle interferes with the measured velocity.

Any recomendation on how i could connect the above in order to avoid the measured velocity being dominated by the road test angle?