Sweet ride. You have way too much weight with the HD, that is the problem, and you had 60 whp less too. It was bound to happen. The HDs are sweet trucks but they weigh so much. I was heavily considering a Lighening myself before I got my Cobra, and the L's with the much smaller cab weight almost 5000 if I remember correctly.
Do you have a smaller top pulley too? I swapped mine oput and got tuned with just an intake and cat back and I put down 466 rwhp & 474 rwtq. I would expect you to have more power with the port and lower pulley (granted your tq is pretty kick ass).
In the end, your truck will last longer than the chebby anyway.