I bet some time at a scale fine tuning the WD will help. You should restore all lost weight from from axle. The Timbrens have that difficult to estimate by fender height. Also, if you have the Reese dual cam, it is very picky about the cam lobes being centered in the detents of the bars. I pulled my TT at up to 7000 pounds with a 2003 F-150. Depending on how I adjusted the WDH, it could be scary at 60mph or stable at 75mph.
I have a feeling your as equipped payload is lower than 1600 pounds. Confirm with driver's door Tire and Loading sticker.
