Today, I was told about a situation where when filled with 6 quarts of oil [the correct amount with new full sized oil filter], the truck's engine registered about half way between 1 qt. low and full. This has been discussed previously on our forum, but I think it will be easier when searching if the subject is specifically about this topic.
I have owned 3 Ford trucks and have found that when filled, the dipstick did not reflect the 6 quarts as being full.
Next time you change the oil, park on an even surface and make sure all oil has drained. I usually start with a warm engine, remove the drain plug and then grease the front end and u-joints and check the air pressure of the tires. That gives plenty of time for the oil to drain before replacing the drain plug. Next, remove the oil filter and replace with a new one with anti-drain back check valve [i.e. Motorcraft FL-1A]. Pour in 5 quarts of appropriate weight oil [let the oil containers drain well] and start the engine, keeping the speed as low as possible until oil pressure builds. Let the engine idle a few moments and check for leakage at the drain plug and filter. Shut the engine off and wait a few minutes to allow the oil to drain into the oil pan. Now, remove the dipstick and on the back side, using a very clean file, scratch a line where the true 5 quarts of oil leaves its mark. This will now be your engine's true "1 quart low" mark. BE SURE TO WIPE THE DIPSTICK WELL, SO NO METAL FILINGS GET INTO THE ENGINE! Next, add the 6th quart and repeat the above process, marking the true "full" line on the back of the dipstick.