I had the same intermittent "Shift to Park" problem early this year. My warranty had expired so I figured out how to fix it. It is a pretty simple problem to fix. I noticed that if you are in Park and you look on the dash where the gear indicators are, one gear is red (the selected Park gear) and the others are grey. If you push the button on top of the gear shifter (whether you shift it or not), the red P changes to grey. When you let the button out, the P changes back to red. When the shift to park problem happened, the color stayed grey whether I pressed the button in or released it. If I released the shift button gently, I could get the P to stay grey but if I released the switch firmly, it would usually change to red like it should. That told me that there must be a switch that is failing intermittently in the system somewhere. I found the little switch in the gearshift assembly about 4 inches below the shift knob. Unfortunately, Ford does not sell that switch as an individual part; they want you to buy the whole shift knob assembly which is about $130 if I remember correctly and includes a new switch. I checked the switch closely and it had the name Omron on it but no other identifying info. It took some digging, but I was able to find the exact switch and buy one online for about $10 delivered.
Here is the switch info so you can buy one if you need it:
Omron part number: D2HW-BL201H
Mouser.com part number: 653-D2HW-BL201H
Mouser.com url:
http://www.mouser.com/ProductDetail...DBhwQjHSWg==&gclid=CNDGpqCk-soCFQkwaQod70QATQ
Getting to that switch was not too bad, but it is a bit too much to try to explain that in this post. The service manuals explain how to get to the base of the shift assembly. It took me about an hour or two to get to the switch the first time but I was being slow and careful. I did have to solder the wires that were on the old switch to the new switch, so you will need minimal soldering skills to do this job unless you just buy the whole shift assembly from Ford. Additionally, I was careful to only allow the wires that connect to the switch to come into contact with the soldering iron or each other. I don't know what would happen if they came into contact with the grounded chassis (probably nothing), but I didn't want to find out. You have to remove the little lever from the old switch and place it on the new switch so that it works in the gear shift assembly. The lever is not glued in; I used needle-nosed pliers and it just pops off the old switch with a little tug.
After replacing the switch, the "Shift to Park" has not returned and that was over 10,000 miles ago so I know this fixed it.
I hope this explanation helps.