I have a Hyster E50 XL 48 volt EV-100, that will not back out of a trailer or start up an incline from a dead stop. Items that have been checked/replaced are : Drive Motor, Start Switch, Potentiometer, Traction Card (all settings verified at factory parameter) conductor, all contactors assys are in good working order. Battery is fully charged and in good working condition. The lift will take off fine on level surface, just not on incline. Any suggestion would be greatly appreciated. Thanks!