I have a Mahindra 3616 that is losing power when I go up a hill or now attach my finishing mower. The Engine remains at rpm's and sounds strong, but the tractor just slows down and stops. If I wait it will gradually start to move again but slowly. It is a shuttle shift. I have changed hydraulic oil and filter, fuel filter and air filter which did not help. I am thinking it must be a hydraulic issue maybe pump or relief valve, but I do not know. The tractor has around 400 hrs on it and problem is gradually getting worse. I am now down two gear positions where I used to run. Any ideas what to do or check next?