Hi goncalosousa;
The hydraulic engine's accelerator controller is operating on a pressure differential between the rod end and barrel end of the cylinder. This pressure difference is controlled by the item you repaired that leaked.
With the engine and hydrostatic drive at operating temperatures and your truck's pedal adjustment unchanged from before the leak was repaired, and engine running, brake pedal applied, depress the FWR and REV pedals fully. Then with the pedals released, pull back on the lift lever. Hold lever in position for a moment and then release.
The speed control servo cylinder moves the injection pump's lever to the stop each time, and the engine attains the upper speed of 2250 (+50) and then drops tp a low idle of 750 rpm. If this is not occurring a check of the entire hydraulic engine speed control will need to be performed to isolate and clear the cause.