Just do a search for "door crack". basically if you start at the rear view door mirror standing outside looking at the door, move along the window bottom rubber, then go about 1 inch or so up the rubber on the end above the door handle. Pull back the window rubber on the outside and you may see a crack there. It looks like a hairline fracture crack. Usually it isn't visible until you pull the rubber back.

Here it is: https://www.f150online.com/articles/cracks.html (with pictures)

 

I have a 2003 Super Crew 4x4 with the 4.6 auto and I have not regreted this purchace at all. The 4.6 is plenty strong and hauls my truck no problem. I didnt test out a 5.4 because of the slight decrease in gas mileage, no real need for a bigger engine, and it being slightly more expensive.

 

I had the 5.4 in the Super Crew 4x2 and i liked it did not like the gas mileage though.I now have the 4.6 in a super cab and its pretty good.Not as powerfull ad the 5.4 but good enough I dont do any towing so im satisfied