I just had this happen to me yesterday in my driveway to my 2004 Crewcab Lariat (5.4 V8) as I pulled in and put it into park. It actually stayed in neutral and started rolling backwards. The gear shift handle had no resistance as I moved it through the gears and I could not start the engine. Upon checking this site and then checking under the vehicle the end of the shift cable had come off the trans and the bushing inside the fitting on the end of the cable was gone. I found a replacement bushing set at Advance Auto for $8.00. ("Pedal and shift linkage bushing kit", part # 14041 - go to their web site and search "gear shift bushing")
The package has 5 bushings in it. The next to largest of the three that look similar is the one that fit my truck. It snaps into the cable with a pair of pliers (The "pointy" end of bushing goes in first.) and then I snapped the whole thing back to the tranny with the pliers also. It fit snugly and had a good solid feel to it when it did. Make sure there are no small pieces of the old bushing still inside the cable end. I had to scrape some out before the piece would fit correctly. Also, the flat side of the bushing will fit completely inside the cable end when snapped into place. At first I thought the large bushing in the package might have been the right one but the flat side did not fit inside the fitting on the end of the cable so it would not snap into place.
The job took me about 5 minutes and I'm a novice.
I bought the truck new in 2004 and after 10 years and 125,000 miles I figure it is probably time for stuff like this to start happening.
Thanks dramas. Had exactly the same problem yesterday. Picked up the bushing replacement kit you referenced at AutoZone and found that the "correct" size bushing for my 2004 5.4 FX4 was the next-to-smallest of the 4 look-alike style bushings. After removing deteriorated fragments of old bushing from the rubber cup at the end of the shifter cable, the replacement snapped right in to the rubber cup with a squeeze of the pliers. Snapped the new bushing onto the tranny shift lever with another squeeze of the pliers and it was "good to go".
Appreciate your post which saved a couple of hundred $$ in towing charges and probably the cost of an entire shifter cable at my local repair shop.