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loss of power when cruising
I have a 2004 F350 6.0L diesel auto with 225,000 miles. I'm pulling a 9,000 lb trailer, and experience a loss of power in the upper gears when cruising at higher speeds.
I use "tow/haul" option, which is very nice. For the 1st 3 gears, she wants to stay in gear until around 2.5K to 2.8K RPM before shifting to the next gear. In these 1st 3 gears, it feels like the truck has a ton of power.
The problems occurs when I'm in the highest gear, and approach a slight incline. I will start to lose RPM's until it gets to around 1.8K RPM. If I then step on the gas pedal, it then blows black smoke, and does NOT shift down. Then, I'll take my foot completely off the gas pedal for a second. Then, I'll step on it again. Now, it shifts down, and, as long as I'm giving it a lot of gas, it'll stay in the lower gear until I let off the pedal, or, it reaches around 2.5K RPM.
After it shifts down, if I'm not real aggressive with the gas pedal, it will shift into high gear at only around 2.1-2.3K RPM. This is way too soon, in my opinion, as it then drops to around 1.8-1.9K RPM, and I have little power again. In gears 1 thru 3, it seems to stay in gear until at least 2.5K, no matter if I'm accelerating or not.
It acts the same way when I'm not pulling something. If I go up a slight hill, it'll blow a little black smoke and hesitate. I then let off the gas pedal completely, then step on it to get it to shift down. Doesn't seem like I should have to do this.
So, is something broke that tells it to shift into the highest gear too soon? Or, it's not shifting down when it's under load?
Or, is my engine just low on power for some reason...
I get 11 MPG when towing. 16 when not towing.