The shift linkage is pretty simple. Like Themightyquinn said, just disconnect the shifter linkage at the transmission (just pop off the ball joint) and see if the cable feels free. That would tell you if the cable itself is binding up, in which case you should check for mechanical damage to the cable and sheath.
If the cable moves freely, then your shift linkage may be out of adjustment. There's an adjustment lock clip (white plastic) near where the linkage connects to the transmission that you can unlock by pushing it up out of its groove. Once that lock clip is fully disengaged you can slide the adjuster back and forth. You would want to synchronize your shifter inside the cabin and your shift arm on the transmission this way. Standard procedure per Ford is to put a 10lb weight on the shift lever while it's in Drive, put the trans shift arm on Drive, then connect the ball joint and lock the adjuster clip. I have had better luck adjusting it in Park though, as synchronizing the linkage in Drive caused binding. I simply set the inside shifter and trans shift arm both to Park with the cable adjuster clip unlocked, then attached the ball joint, then locked down the adjuster clip. Fixed my linkage problem, as it was hard to pull out of Park before.
