What is the true difference between the 2500 and 3500. I have a 14K 5'er and currently pull it w/ a 2500. I am thinking I should be pulling it w/ a 3500 and I really want an 06 mega. What are the real differences between the 3500 and 2500, besides springs, that would justify me buying one? Or could I just do a few things to my 2500 to meet the same standards of the 3500 rendering the 3500 mega a nicety? My sig is current