welcome to the forum jeraco. 
 The 3.5 EB engine and 3.31 gears and the 6 speed tranny will have no problems pulling that trailer. 
 The number you have to watch is that small 3800 RAWR Ford uses with the 6800 gvwr package. RAWR can be the lessor rating of a tire...wheel...rear spring pack....rear axle. With this trucks 6800 gvwr and 3800 rawr numbers its rear spring pack. 
 You have the truck so drop by a set of scales and weigh the trucks front and rear axles. This will tell you to the lb how much weigh will be in the bed and on the back of the truck. (example) Your trucks rear axle may weigh in the 2400 lb range which leaves around 1400 lb payload on the rear axle. 
 These numbers along with a weight distributing hitch mfg instructions can also help in setting up the WD hitch and dialing it in.