Just bought a 2006 Ford E350 60k miles 5.4L V8 engine automatic, drove it back about 1000 miles on the highway, no problems. Smooth as butter, no noise accelerating, perfect handling, etc.

I am staying temporarily in the mountains, and the first time I drove it up the mountain, it struggled. I never went above 15-20mph, and went down to 5-10mph at times. The next day when I drove it down (in first gear), it went into limp mode (not going above 10mph in D) and I towed it to a shop. At the shop it was working fine and they test drove it up to 55mph, not sure what happened.

However, it no longer runs smooth. Harder start, accelerating is a bit rougher and noisier, there's a "whoosh" sound when I press the brake pedal (it disappears when I depress it fully, and braking works fine). The second time I drove it up the hill it seriously struggled, and I had to pull over and restart a couple times. Not driving it again, it's parked here until the day I either figure out what's wrong or drive it straight to a shop.

The only other issue I can think of was that on a cold night (33F), the exhaust pipe was putting out cloudy smoke when I idled for an hour. However, it did not do this when I was driving, nor when I was idling during the daytime when temperatures were higher. There is a lot of rust on the vehicle underside, doesn't bother me, just thought I should mention that.

Any ideas what could be wrong? The mountain is very steep, the steepest I've ever driven on, and part of it is dirt road, but I was very careful driving it, never pushed it (even going 5mph when others were passing me) and used lower gears to come down.

(Oil and coolant levels are fine. Shop checked the transmission fluid and said it was nice and thick and not low, though it seemed a little low to me when I checked but I'll trust their judgment. It never had any check engine or warning lights.)

 

If,,,,,,,,,,,,,it is going into "Limp Mode" the computer system is detecting a problem that gets reset after you turn the ignition off and restart the engine.

If this is what is happening a scan tool needs to be connected and checked for codes before you turn the key off.

Again,,,,,,,,,,,,,,,, if,,, this is what is happening whatever is causing it to go into limp mode will need to be found.
We don't know much about the history of this vehicle. Did it set a long time before you purchased it? It may be starving for fuel, we don't know.
Suggest you consider a thorough service consisting of ,spark plugs, fuel filter, and a good oil and filter change.

 

I would look at the live data displayed on the scan tool as the engine is sputtering.Sure does sound like a fuel pressure issue to me.