I never said newer automatics couldn't haul, but these new 6-speed autos especially when behind a gasser than can spin 5000+ RPM, you have the option of 3 (or 4) gears at 55-60MPM: Overdrive, (overdrive #2), Direct (or close to it), and a reduction gear.
Putting down the hammer in this situation you don't know which gear it's going to land in unless that auto has a manual gear selection option. I was talking of the abilities of a manual to hold a gear in that respect, because you know it won't shift. If an automatic does have than manually controlled option, then it essentially has the properties of a manual transmission in that situation.
My "rig" which is a HUGE 1999 F150 has a 5-speed. I've put it on the floor a few times, let that little 4.6L spin to her heart's content :-)