Loss of MPG? what gives?

[mstan]

Guys, question is, what would cause my 6.0 to begin dropping MPG. it is a considerable loss. 2005 F250 FX4. K&N Air intake and filter. Magna flow SS exhaust. Juice edge. I purchased this truck new and have kept records on it since new and all maintence is up to date. Before the sulphur removal from the diesel I could expect 20-21 mpg at 70 mph on the interstate. I tow a 36 foot fifthwheel which is about 14,000# loaded. I could expect 13-14 depending on conditions towing.
Currently this past week I got only 8 mpg towing and running empty 70 mph I was only able to see about 15 mpg. If I was only losing a 1-2 mpg I would expect it and move on. But this stinks. Anyone have a idea?

Thanks, Mark

[closh]

This is interesting because I am seeing the same thing with my truck. I have lost about 3-4mpg over the past 2 weeks. Quality of fuel??

[mstan]

It has to be a fuel issue I would think. I changed the fuel filters thinking that I might have picked up some trash. That did not fix the problem.