Those TB spacers don't do anything for fuel injected vehicles. They help a tiny bit on throttle body injection and carbs, and I do mean a tiny bit. The only tests done that show an improvement are conducted by the company selling the product, and they are hardly an independent source.
I'd unload the K&N filter, they don't filter the air as well, and the first cleaning can cause engine problems if you aren't very careful about oiling the filter. Too much oil will foul the MAF and cause the engine to run poorly. On the Chevy trucks (my own forte) fine dust is usually found inside the air intake hose after the filter when a K&N is used. MPGs aren't affected either way (paper vs K&N), either. I did the K&N because of their claims, and got rid of it because of the reality.
Not familiar with the Ford trucks, do you have an electric fan or clutch fan on that truck? Chevy has proven that electric fans do just fine with towing heavy loads, as they are selling them as OEM equipment on their trucks now. You can either try to run a Chevy fan set, or build yourself a fan shroud and get aftermarkets. A lot of the Chevy guys are also running Taurus 3.8L twin fan sets on their trucks, with some of the trucks being supercharged 350s and 383s with no overheating problems. I saw a solid 2MPG improvement on mine when I added them to my 96 Tahoe, and my S15 2.8L with a single electric fan added 5MPG on the highway MPG. Not to mention the increase in power over 2500RPM. The mechanical fan is a huge drag on the engine. On top of all this, having an electric fan will also allow a faster warmup in the wintertime by not forcing freezing air over the engine when it's cold, which will allow closed loop operation a lot sooner.
Another thing you can do, long tube headers. They will emphasize low end torque, which is what you need in a truck. And, as you will normally be cruising at a low RPM, this increase in torque will only help. Go ceramic coating to keep underhood temps down and help fire the cat faster.
Course, had you just bought a Chevy Duramax to begin with...