Zero Turn Mowers

From the moment i purchased this zero turn i had problems off and on with the deck spring coming loose or the deck belt jumping off. Usually the deck belt would come off when the PTO was engaged and on occasion it would jump off while cutting. The deck tensioner spring would come unhooked at random. Recently its gotten worse. I have put new blades on it and replaced the deck belt. I am having alot of vibration in the tensioner as if its not tight enough. When i purchased the mower the I-Bolt was tight about halfway down the threads. Now i have it tightened all the way to the eye and it still isnt good enough. I just installed a new spindle because it appears one of the blades got loose at one point and wore down the star on the bottom of the spindle so that the blade wouldnt lock in place.The other spindle feels tight and has no wobble. I checked the bearings in the tensioner pulley and it feels tight with no wobble. This is the third deck tensioner spring i have installed on the deck in two months because the springs keep breaking at the hook. This is getting very frustrating to say the least.

Any suggestions?