With 4.56 gears you would be in third gear on hills and probably right around 3800 rpm which is in the powerband for the torque.

 

I think you will be towing uphill in 2nd at whatever speed you choose, but with pedal left instead of being floored.

I dont see a gear change letting you walk the hills in 3rd. Your truck won’t have the torque to make that happen.

 

I’ve not been able to find a 2006 E-Series brochure on line. Other sources suggest the OP’s E-350 passenger van is fitted with a 2V 5.4 V8 and a 4R100 four-speed AT. He’s already indicated that his van’s axle ratio is 3.73. Tire size is unknown. The mid-2000’s E-series 5.4 was rated at 255 HP @ 4500 RPM, and 350 lbs-ft torque @ 2500 RPM.

These specs may help assessing the OP’s configuration and offering performance-improving suggestions.

HTH,
Jim / crewzer

 

Tire size is 245/75/17. A little over 1” in diameter larger from stock.

 

Larger tires mean fewer engine revs per mile. It’s the same effect as lowering the axle ratio.

HTH,
Jim / crewzer

 

I towed with vans for years.

The 5.4 was never a great towing motor. It needs to turn rpm to make power. So gearing is critical. 3.73s with taller than OE tires are creating much of your problem. Either shorter tires or shorting gearing or both.

The "chip" may actually result in less torque. I would try it without and see if it tows any better. I have heard good things about 5-Star tunes for these but have never tried one myself.

And have you had the catalytic converted checked? Its a common problem for the cats to become partially restricted and it kills the engines power, especially low rpm torque.

 

i asked my mechanic if he thought the cats might be clogged and his response was that if there was an issue with them, there would be codes and a check engine light on. What are your thoughts about his response?

 

FWIW, on my 01 E-150 with 4.6L V8, we put 410 gears on. made a huge difference pulling a small trailer up and down the hills of TN. OH and it has 330,000 miles on it (some engine rebuliding happened and a new tranny at 120K)