Funmobile
Why did you do that? Unless you were going for performance, those don't go bad.
Where did you come to the conclusion that MAF's don't go bad??? They are a very reliable component, but they most certainly do go bad. I agree that if you go to many Ford dealers and they find the MAF is dirty (over oiling a K&N filter) etc, they will just replace it with a new one rather than trying to clean the old one...but that does not mean they never go bad.
Even if he did replace the MAF, he indicated that his truck is stock, so I would assume his new MAF is an OEM replacement MAF and he is running the stock injectors.
I think it's a bit of a leap to assume that he replaced the MAF with a performance unit, and that is the cause of his poor mileage.
90% of all gas mileage complaints are caused by simple things like tire pressures brand of gas used, and even more so by driving habits.
As an interesting side note:
Alcohol is a cheap way to increase octane but E85 fuel (85% alcohol, 15% gasoline) will result in about 20%-25% less fuel mileage...so the more alcohol in the fuel, the less gas mileage.
Now days most regular gasoline contains up to 10% alcohol. Since they cannot add more alcohol to increase the octane many brands use other additives and less alcohol to increase the octane in their premium gas blends. I don't know which brands use less alcohol in their premium blends, but I think this is probably why people claim to get better gas mileage with premium gas than regular.
During the gasoline crisis I have purchased some cheaper No-Name premium gas for my car and I can see a decline in my gas mileage compared to the better known brands like Exxon, Shell, or Chevron, so I suspect that some cheaper brands put more alcohol in their premium gas (not to exceed 10%) than the brand name gas stations.
Now the government is pushing the gasoline companies to increase the alcohol content of regular gas up to 15% which can damage your fuel systems if your vehicle is not E85 fuel compatible. Car manufacturers are already saying that if the alcohol content of gas goes up to 15%, they will void your new car warranty, and you will get even worse gas mileage !!
...Rich