My buddy has been running nothing but 3" heavy waterfowl loads out of his ever since I sold it to him in 1987. No problems. I don't think I have ever seen a problem I would attribute to heavy loads. The gun doesn't really care what's exiting the barrel as long as you have the right tubes for steel or whatever.
Why are you shooting all that stuff in 3"? Do you just like a lot of romp and stomp on both ends?