I have a Duetz-Allis 5215 ,that I purchased last year . I love the tractor but after a few hours of work , the hydro transmission slows down , My question is who rebuilt your hydro trans , and where did they get the parts . I might have to have mine rebuilt . Now for your question , you might have air in the system that you will have to work out by shifting the lever through all gears including your high , mid and low shift lever . sometimes air gets in the system and is hard to get out . I have had to work new power steering pumps back and forth in order to get the air out . I have also had to work the shifters back and forth after I have rebuilt various transmissions . All hydrolics sometimes get air trapped inside ,to include brakes .Hope this is the problem , instead iof a teardown