Hello and welcome, this is a common problem on the 550,450, 400 as the sistem is the same. Its not only the brake cable adjustment, the gear selector inside the gear box is tight as it works with springs and gear selector. You can check the brake cable pin on the shifter and see if its really to out. It has a welded nut on the shifter base and the another wich blocks the cable pin. There are very tight so be carfull to loose them. You can pull back the pin a bit, so you don't need to step on the brake pedal so much. The low gear could be a shifter linkage adustment, but give it a time to breake in before you make any adjustment. Lubricate all the moving parts on the shifter to get better results. Here some pic'sss