I agree with the point that a manual can handle it with a skilled driver, and that Ford's limitation likely comes from not wanting to replace clutches under warranty, but I'd be cautous about the legal issue and personal responsibility.

A couple of examples, although not exactly the same situation but still somewhat the same principal, are what I base my opinion on:

In Oklahoma there is no law that says you can't exceed the horsepower rating on a boat, (ie: putting on a bigger outboard than it was rated for) and you can't be issued a citation for Insalling or using a bigger motor. However, Oklahoma Lake Patrol officers (which is part of the Oklahoma Highway Patrol) have told me that if there were ever an accident involving that boat, they would cite for careless/reckless driving based on the oversized engine.

Oklahoma permits light trucks to pull two trailers. (such as a travel trailer pulling a boat trailer) The law only specifies overall length and weight. However, Highway Patrol officers will tell you that if the first trailer is not a 5th wheel (both trailers bumper pull), and you get into trouble, they will cite you for careless/reckless driving.

Even though I've been told this, I don't know anyone personally who has been cited under either of these situations or the one that's being discussed in this thread. In reality, I've seen overloaded trucks with thier rear bumpers dragging and thier front wheels barely on the ground drive right past a city police car and OHP with out even a second glance.

But anytime I decide to exceed the numbers that are stamped right on my door jamb by the manufacturer in plain sight, (and yes, I do exceed them sometimes) I realize and understand that I'm taking responsibility for whatever happens, whether its an accident, ticket, or burned up clutch.

 

The clutch issue on towing capacity is a real concern at Ford I think. However, a good driver will have no problems. Perhaps another reason is that the automatic downshifts when load and rpm require. A 5 speed driver could seriously "lug" the engine if they don't downshift as appropriate. Long uphill grades at highway speed may require a downshift to 4th or even 3rd if the grade is steep enough. I'll keep my 5 speed though. We just came back from towing a trailer through the rocky mountains with our V6 5 speed and it did just fine. I find the real problem with the 5 speed is backing with the trailer. Ford had their head up their a$$ when they selected the ratio for reverse. It is WAY too fast requiring you to slip the clutch a lot when backing.

 

Very good point acadianabob, lugging an engine is extremely hard on it adding to more uneccesary warranty claims for Ford.

 

RASCALLYONE,
I've got a 4.6, 5-speed in my F150 4x4. I've found that putting the truck into 4 wheel drive to pull my boat out of the water and up the ramp works pretty well. Seems to be much easier on the clutch. The boat by the way is an 18' inboard, approx. 3,000 lbs. with the trailer. So far so good.

 

I am one of the people that has towed significantly past the rated towing weight of a manual truck (but not over the rated cap on a similarly auto truck).

In some cases I think the manual is better. Compression braking is better on rare occasions than the brakes. During transitional maneuvers staying in a particular gear at part throttle can be beneficial. Even the best auto just can't anticipate your next move. Much less trans heat is generated during heavy throttle operation also.

Personally, if you decide to tow like you had an auto I’d just take a wait and see approach. If the clutch wears prematurely, then put in a better one. I never had any trouble with my 5000# load. Good thing the safety police didn’t catch me without my Auto trans.