A different approach should be to utilize a variable displacement pump.  Once the pump is configured for reduced displacement, it makes a reduced quantity of oil circulation, leading to the hydraulic motor(s) to show much more slowly. A CVT operates employing a process of pulleys and a belt or chain. https://gearboxcvt17272.blogocial.com/top-latest-five-gearbox-cvt-urban-news-69917316