hydrostat

Hello, So I have 2013 G3038H tractor with about 1050hrs on it, and the tractor moves so slowly now - in all gears (high, medium and low). Fluid is not very old, and still looks clean. I changed the filter recently and cut it open to see if there was any metal debris in it - but it was clean...

I've dug through the forums here and even read some scholarly articles on the subject but I still don't understand how revs affect the performance of the HST when using hydraulic implements like a loader. I can feel the difference it makes in pulling, cutting and ground engaging implements but...