The loader is rated at 600 LBS to full height. However, it will lift more than that providing the tractor is properly weighted.
First off, the tires can be loaded with RimGuard and triple wheel weights can also be added to increase overall stability whee it counts. Then a very large counterweight can be added to the rear. Some owners have put 500 LBS back there and claim they can lift 1000 LBS with the loader.
Do not worry about the front axle because it is designed to handle 3000 LBS of static weight.
As for your other problem, that is probably in the foot pedal linkage. Drop me an e-mail and I can hook you up with a document that explains what needs to be done.