I havent read this entire post so if this is repetitive I appologize
I have a 2010 PC2350 on an E450 chassis. I continually run in and out of tow/haul depending on conditions whether Im towing or not. Even so, the thing was way underpowered IMHO, the biggest problem being that it went straight to third as soon as it started up even a slight grade, so I did the following with excellent results:
1. Banks cat back system
2. K&N Air intake system (not just a filter - includes larger intake pipe)
3. SCT down load - includes code reader that stores factory setting. (Tell Mike what you are trying to accomplish and he will set you up.
As I recall I spent around $2000 for parts and did the work myself. I had to cut the old exhaust system to get it out as well. The reault was a considerable increase in pulling power and acceleration. It now has the power to pull grades in 5th, 5th TC lock up, and 4th that used to send it straight to 3rd at 5000 rpm which was completely unacceptable. The intake and exhause changes are obvious. The SCT down load changed fuel/air ratio, TC lock up, shift strategies, timing, etc.
For a little perspective, when towing my little trailer, my front axle tips the scales at 3,300lb, rear 12,100, and the trailer axle is at 2,200. I think my tongue wieght is probably around 400-500lbs.
So pulling a grade in fourth, im runnng at around 3600 rpm at 60 mph rather than just over 5000 in third, which I refused to do, so prior to the mods I would end up running around 45 to 50 max. TC lock up takes me from 2200 at 65mph to around 2700 in fifth. Ford apparently programmed these things to skip fourth when downshifting because the fifth and fourth gear ratios are somewhat close, but with these mods you can coax it into fourth and keep it there with some practice for a much more enjoyable run up long grades. I wish I could just shift into fourth like I can with third, but this works out quite well as long as you pay attention to the grades, throttle demand, and the tach.
All that said, on the way to Vail on I-70 from Utah, hauling a 2200lb trailer, it still went to third on the steeper sections. Fooling around with non-scientific experimentatin, i achieved about a 4 second reduction in approximate 1/4 mile times (:18 vs :22). The only down side is that when its pulling a grade in fourth (again something it was unable to do before) the intake is LOUD. Im going to add some sound deadening to help with this but I really dont mind since the power increase was so pleasing - far better than expected.
The E450 has 4:56 gears which helps some, but not nearly enough without the above mentioned mods, and it rides way too rough - air bags are next.
Hope this helps