Agree with simple solutions first. Ditch some of the weight - mentioned in previous post - and see what happens.
Think of it like this. How much of the 30 horsepower is taken up running the finish mower? Who knows, maybe 15? So you really only have the other 15 to move your multi-thousand pound rig around. No wonder why it's kinda slow going uphill!
Removing the loader is the easiest way to shed some weight. Factory loader was designed for easy off/on; if you haven't done it before, study the manual and practice some. Probably at least 700 lbs.you'll set aside before mowing!
Even without the loader on, you have a heavy tractor with modest horsepower. Do you really need loaded tires? If not, that's another 900 pounds of dead weight being lugged around. May be hard to remove, but taking almost a ton off the tractor when mowing will mean the tractor doesn't have to work so hard.