I have an '07 Dodge Ram 1500 with a Hemi engine, and I've been told I could easily pull a 4H slant with LQ on the gooseneck attachment. However, right now I'm using a BP hitch and can only pull so much because the hitch itself can't haul as much.
You make a good point. Newer trucks can generally tow more, due to growth with technology & eficiency.
If you ever have any doubts, having a general inspection at the local mechanic isn't usually to pricey and they could tell you a lot!