The 2008 source book reads:

Package includes.

- Class IV frame mounted trailer hitch receiver
- 7 pin wiring harness
- 4 channel auxiliary transmission oil cooler with 4.3L V6 engine
- Upgraded radiator and 9-channel auxiliary transmission oil cooler with 4.6L and 5.4L 3V V-8 engines
- 11,000 lb. trailer tow capacity when properly equipped
- Optional heavy-duty 72-amp-hr. battery

 

There are also Heavy-Duty versions of the F-150 too, instead of just having the tow package. Some have the bigger Super-Duty type mirrors on them. Those sometimes come with a 4.10 ratio in the differential as well. Also 7 lug wheels instead of the regular 5 lug ones like what's on my truck. My 2007 is a non-Heavy-Duty with just the regular tow package and I believe it comes with both a 5 and 7 way plug-in which is pretty much all the tow package gives you, among a few other minor things like what green crew above me said. The Heavy-Duty versions bump your tow rating up about 1,000 lbs. or so.

 

I don't believe there is an "HD Towing" package. You can get the towing package, which upgrades to the class IV receiver, aux trans cooler, 4/7 pin connector, 72-amp battery, etc. You can also have an HD payload truck package which has 7-lug wheels, 4.10 gearing, upgraded suspension, etc. You may end up with an HD F-150 with trailer package, but there isn't an HD trailer package to my knowledge. It's picking nits, but I'm just trying to clarify.

The trailer tow mirrors are separate from all of the above and is an individual option. My truck had them from the factory, but it's not included with the trailer tow package or the HD package.

 

Yeah, I know what you mean. Basically what I was saying is just having the towing pkg doesn't make it "Heavy-Duty". I may have worded it wrong (sorry for the confusion), but that is what I meant. My 2007 is a 2wd ext. cab 5.4 with a 3.73 ratio and the towing pkg, but it's 5 lugs per wheel and my tow rating is 9,500. GVWR is 7,050. The HD will take a little more trailer tongue weight than the 5 lug ones and raise the tow rating some, I believe.

 

You should check your wheels. You're missing a lug, you should have six.