I know where you are coming from on looking for a truck. My F350 is also a 2011. It has just under 120,000. I just replaced all the belts and pulleys. I am doing the upper and lower radiator hoses today. It has had a coolant smell for awhile, but I can't find evidence of a leak anywhere. These Ford 6.7 diesels have 2 coolant systems though and I suspect there is a small leak in the secondary system that has small hoses going everywhere; turbo, trans cooler, power steering cooler, intercooler, fuel cooler, oil cooler and it's own little radiator.
The fuel gauge stopped working 2 weeks ago. That is a "drop the tank" job, which isn't too bad, except the sending unit is built into the pump starting on the 2011. The sending unit/pump is $250 instead of $35 for the 2010.
All in, the truck still runs great and should have lots of miles left. It's paid for, tows anything well and it's still cheaper to fix the little stuff than have another truck payment for now.
As far as moving up to a 250(0)/350(0), like others have said, they will tow much better. They will just feel more stable. With a 5500 lb trailer, you would barely notice it was back there. When I went from an Explorer to an F250 diesel, I didn't need WD bars or the dual sway controls I needed towing the 6500 TT I had. The problem was, having a much more capable TV led to getting a much more capable camper.
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