Rear Suspension

any one have an idea what i can do for the rear shock. I am 300lbs(yeah i need to lose weight but i am 6'5") is there a shock from another bike that will work better or do i need to buy something new.
Anyone here of a company Wilburs that does rear shocks they have decent prices ($550) but they say every 20-30k miles it needs to be rebuilt at $100????

check out the penske's on the lindemann engineering site. Best shock in my opinion