2006 Expedition towing
 

EddieBauer Edition with the tow package. I recently had the spark plugs changed because of a misfire. I have also used 2 bottles of Sea Foam to help clean up some of the carbon. Problem now is when I'm towing my boat I don't seem to have as much power as I need. It's a 5.4L and the boat weight is under 2,000 lbs so it should be able to tow without a problem. There's no sputtering or engine noise. My owners manuel says to tow with the overdrive off if the vehicle shifts gears repeatedly. What it doesn;t tell me is how fast I can drive with overdrive off. I have used this method up to 50MPH and it works well. So my question is with the vehicle and engine size should I have more power than I'm getting or do I use the overdrive option more.
Thanks