there was a bulletin about this a number of years ago
I'll paraphrase
assuming your parking area is perfectly level of course.
step one adjust the tire pressures to recommended by the book. Depends on what tires you have too, some are 20 rear/35 front, others 15 rear, 25 front, etc.
if this takes care of it good if not keep readin
two, check all the hardware for tightness. That's actually a service item.
Thirdly if all of that has failed to correct the issue the next step is more involved.
Stop engine,set the park brake remove the key and hang a do not operate tag on the steering wheel. Lower the loader to the floor with the bucket level front/rear (so it's flat on the ground). Now loosen each of the loader main frame attaching bolts but DO NOT remove them. Just loosen em a turn or two. Now carefully get back in the seat, start the engine and apply down pressure to the loader, not enough to actually lift the tires off the ground but enough to take some weight off of them. Leave the down pressure on the loader, turn the engine off and remove the key again. Make sure you lock the loader control in the "locked" position before leaving the seat. Then go torque all of the loader main frame bolts to spec while maintaining down pressure. Now, get back in the seat, unlock the loader and allow the loader to settle with no pressure by moving the control stick in all directions. Start the engine and then work the loader up/down a few times. Once you do that, let the loader settle to ground again but with NO pressure on it, just let it's weight settle in the float position. Turn engine off, then go re-torque your loader mainframe bolts.
If it's still not level, you can put a block under the low side to help tweak it the other way while the bolts are a little bit loose.
If all that fails you will have to consider that the loader is not a skid-steer, nor is it a bulldozer--both of those tools are specifically designed to be flat side to side, and are adjustable to achieve that. A tractor/loader is kind of a "do most jobs well but not one job great" type tool thus if you can't get that last 1/4" adjusted out of it, you probably aren't gonna be able to unless you play with tire pressures on the tractor where one side is higher than the other.
As a drag racer, I've learned that not all tires are created equal; often I have to send one tire back and get another because I try to keep the circumference of both tires within 1/2". I'd like them to be zero but I've not been able to achieve this without staggering the tire pressures. Doing that has a consequence of causing the car to drive left or right which is not good when the front tires are not really doing anything until about 400 feet downtrack and most times are not even on the pavement until 250-300 foot if everything goes well. Similarly tractor tires, it is not uncommon for them to be "off" a little from one tire to another and the only way to know is to actually measure the circumference of each and if they're way off, the only thing you can do is to either replace one of them with one that is closer, or stagger the tire pressures. You're not going 200+ mph like I am and you don't have a locked rear axle, so staggering them is not a big issue.
