DarrinT04

The 3.73 ELD will definitely increase your towing capacity from the other rear ends

smokeywren

Depending on the model year, the 3.73 axle ratio was optional but not part of the FX4 Off Road pkg. On a late-model FX4 Off Road, the 3.73 axle ratio is included only if you have the heavy duty payload pkg (HDPP) or the 2.7L Payload Pkg . So use the axle code to determine your axle ratio.

But it doesn't matter, because axle ratio is used to determine GCWR and tow rating, not GVWR and payload capacity. GVWR (payload capacity available for hitch weight) is your limiter as to max trailer weight.

So download the RV and Trailer Towing Guide for your model year and use the Trailer Towing Selector charts in the guide to determine your GCWR and tow rating. But understand that tow rating is severely overstated for most F-150s.

Note: In my earlier post I had a typo that said you could use the towing guide to determine GVWR and tow rating. That should read that you can use the tow guide to determine GCWR and tor rating, not GVWR. GVWR is on the driver's door post, not in the trailer towing selector pages of the tow guide.