I've got an E99 350 SD that's showing some signs of decreasing performance.
It's a 7.3, factory rebuilt engine with less than 50,000 miles. I keep track of mileage on every tank and right now it's getting an average of 11½ mpg.
It's also started smoking when it's under a load, such as going up a hill when empty. Turning the chip to the heavy tow setting helps with the smoke, but drops the mpg through the basement. I don't have any hot rod settings on the chip. Just economy and tow settings. Interestingly enough, my best mileage isn't with the economy setting. It works best set on the medium tow setting.
Also, when going up a steep hill the EGT usually climbs over 1500°. When I've got a load the temp will top 1700° going uphill. LOTS of smoke too.
Boost usually runs about 8 psi under load and 1-2 on flat ground when empty.
It's also started to get a little hard to start when it's cold, though it always fires eventually.
Oil and filter are fresh.
It's a 4WD with 4:10 gears.
I really need to get this thing back in shape as I drive it a lot in my firewood business, and with the price of fuel I need every mpg I can get.