1st gen lightning frame
 

I am curious to know what the actual differences are between a lighning chassis and a regular f150 chassis. Every where it just said they were "heavy duty"
Thanks,
Sean

The main difference is the thickness of the rails. The L rails were formed from thicker steel. I think there are also some stiffening braces that the std. F-150 didn't get, but I don't remember for sure.

They're the same thickness as the 4x4 F-150's. The L frames also have plates welded at the rear gussets; just above the axle tubes.