2002 f250 sudden loss of power

My 2002 f250 5.4l pickup had a sudden loss of power. After the mechanic changed the spark plugs, air filter, checked the catalytic converter, and de-carbonized the engine it still has no power. It checks out ok on their computer diagnostics and they are stumped. When it first happened, I heard a rattle which sounded like it was in the drive shaft. That stopped the same day but a pinging sound in the engine was present. After the de-carbonization the pinging is a little less but I still feel like I’m pulling a heavy trailer when I am not. The wheels turn freely but it feels like the brake is on or something is still making it feel very sluggish and like it’s lost its ummph. There is no lifter noise, backfiring, missing, just no power. Any ideas?

I think I’d start by putting a gauge on the fuel rail and make sure that you’re getting correct pressure from the pump. It could be something as simple as a clogged fuel filter or a bad fuel pump.

It turned out to be a bad u-joint. The two mechanics couldn’t believe the u-joint would make the truck feel sluggish. However, after the rattle returned, the u-joint was replaced and now the truck runs great.