I think the axle you have is plenty strong. My 4400 has the standard axle and it hauls 4 ton of weight on it pushing and lifting an eight foot wide snowplow. I've been using this truck for 5 years now and never had a front end problem. BUT, I think to swap out a 2 ton front would be a direct bolt in since the fenders and the frame between the two are the same. The main drawback would be finding kingpins available for the bigger axle. I know the 1 1/2 tons are still available.
Just some food for thought,
Scott
