Manual - I don't doubt you have pulled 6k with your 4.2 stick, but the 3500# rating is there for a reason - it's very hard on the clutch and the tranny. Steve83 says he has pulled 10k with his I6 Bronco - this is WAY over the rating, it pulls it, but it's NOT recommended!

It's just not wise to sit here in an Internet forum telling people that they can exceed the manufacturer's rating - from a safety and a liability standpoint, before you even talk about some states' DOT checks. Heck, I'm hanging my butt out in the breeze towing less than the rating on mine because I only have 6000# tags on my truck - GCWR is 7800#.

 

Dude! This is an easy one. Get a newer F-150 with the 5.4L and a tow package. Perfect for what you want. You will not be sorry.

 

Maybe not recommended, but I'd not consider it unsafe. I've found the 4.2l/5spd combo a capable towing package. 5000 lbs hardly puts a strain on the tranny or clutch so I've looked around to understand why it is rated so much lower that the 4.2l/auto. Indeed only observation, but these trucks are plenty strong - I think this is just a gearing issue.....

The 5spd tranny and clutch plate are not weak points - they are shared by other higher rated trucks but, the only apparent difference I could find is that 1st and reverse gear ratios used in these f150's are much steeper than the heavier truck applications. I assume this was a design tradeoff for better gear spread on Ford's low end trucks, and, I think it explains why the manual has a lower tow rating over an auto tranny. The torque multiplying effect of automatic comes into play from a standstill in first and reverse - when you've got to get the weight moving. The 5spd does not have the torque multiplier effect so it got a lower standstill torque rating.

My experience matches this. I frequently pull a 5200 lb trailer. After putting in 4.30 gears, there is no noticeable strain on the drive train. No clutch slipping is required to get underway in first - but backing up can be a pain. Backing a large trailer is slow motion work and this is where I see the 5spd's tow rating (and high reverse gearing) come into play - some clutch slipping is required.