As many have said - ignore the book and know your numbers. When shopping for our F150 late last year, I was extremely picky about what we wanted. XLT trim, minimal upgrades, etc. All of this was because every upgrade comes at a cost of payload (those wonderful sunroofs can cost you a couple hundred pounds in and of themselves). Even the more subtle things like the FX4 package can knock 50-100 pounds of the payload. With all of this as background, my XLT shortbed CC has 1,870 pounds of payload. Many other XLTs on the lot were readily 100-300 below that due to options.
The truck is a towing beast - it doesn't even blink at the 8,000 pounds I put behind it (except in the gas gauge!). It's your payload that will matter. With that trailer your hitch is likely to way somewhere around 1,000 pounds (give or take 100). Add another 100 for your WD hitch, and then add the weight of everyone and everything you have/will put in the truck (including aftermarket adds like bedliners, covers, carry bars, etc.). Compare that total to the payload listed on your yellow sticker and that will tell you where things stand.