4.7L seems sluggish

I have a 2002 Ram 1500 QC, with the 4.7L engine. The truck is not driven that often and when it is, it's all highway miles. There's only 5,000 miles on it.
I took the truck on the road a few months ago and it ran perfect. I got 16 mpg, (travelled about 65) the truck handled great, everything was okay. I hit the road again this past weekend, and the truck seemed sluggish, like it was pulling more than it should have been.
My gas mileage also dropped to 14mpg. I was also travelling about 65mph, same as last time. The engine sounded okay and the truck idled fine (also used 89 octane both times). The only difference was that I lowered the tire pressure. The ride was smoother, but I'll suffice a smoother ride with better gas mileage. The tires say 44psi. I lowered them all to 35psi.
Now, with all the different views on how much pressure should be in the tires, could this be the problem? There is more tire on the road with 35psi than with 44psi, so the truck seems more sluggish? I've heard you should run lower pressure in the tire than the tires say. Is this true? Everyone I talk to says something different. Any ideas?
Much appreciated,
-Chris

maybe the oil in it is sludging up.
j/k they do have a problem with the oil sluding up and ruining the motor though

And the cure to this is what? Change the oil? What causes the oil to sludge up? I use 10W30 in all my vehicles. I have never had a problem. And the truck only has 5,000 miles on it. One oil change so far.
Thanks,
-Chris

Lower than recommended tire pressure is a direct cause for lack of performance and mileage.