Tow Ratings Conundrum

I've been trying to sort out how manufacturers arrive at their tow ratings, and quite frankly, putting a person on the moon must have been easier.  I have a 2003 Toyota 4-runner Limited, 4X4, V-8 with tow package.  I'll be buying a new TM 3023, so I'm sure I have the tow capacity -- at least several of you folks have given me assurance.

But as I look at the specs, I become more confused.  Unless you've recently been on the Toyota website, you'll find they have changed their tow ratings for the 4-Runner (at least those produced after 5/01/03 so the site says).  Used to be all 4-runners were rated at 5000# irregardless of engine.  That's not so anymore.  The V-6 is still rated at 5000#; however, the V-8 is now rated at 7300# (2WD) and 7000# (4WD) both using W/D hitch.  So what might have changed to cause the increase?

The V-8 has less horsepower (235@4800 rpm vs 245@5200 for the V-6); however, it has more torque (320ft lb @3400 rpm vs 282 ftlb @3800 for the V-6).  In terms of towing I assume more torque is better than more horsepower -- is that correct?

For giggles, I looked at the Ford website just to make some comparisons.  I looked at the F-150 and noticed that in going from the V-6 to V-8 the towing rating went from 9000# to 12000#.  Any suggestions why Ford increased by 3000# while Toyota only changed 2000#?

I've also read on "other" RV sites that wheelbase is a big item.  Usually it has to do with conversations about sway.  That makes sense to me -- shorter wheelbases might be more prone to induced oscillations (sway).  But for 2003, Toyota increased the wheelbase (don't know what the 2002 was, but it was less).  Even with the longer wheelbase and greater hp engines for 2003 (before those produced after 5/01/03), Toyota was still rating the 4-Runner as a 5000# tow capacity.  I compared the 4-runner to the F-50 wheelbase (Toy = 109.8";  F-150=119&quot.

So here's my confusion -- 4-Runner V-8 compared to an F-150 has 4 MORE horsepower and 27 MORE ftlb of torque, but 9.2 inches LESS wheelbase so how does the F-150 wind up with almost 3000# more tow capacity?

It's enough to make my hair hurt......

Ed