Is there a difference in size of a full size bed between a F150 and a F250? I tried to install a tonneau cover for a F150 on a F250 and it was a couple inches short. You could put your hand between the rear of the cover and the tailgate top. My F250 is a 1999 model and the tonneau is a 97 - 03 F150 model. Also the width seemed to be a little wider on my F250. When the clamps were tightened down on the rails the bows did not fit snug.
Yes, I noticed a difference as well. I had a 98 F-150 that I would keep sandbags in for winter. I had some wood dividers to keep them in place. I tried to put the wood in my truck and it was too short.
If its a short bed the F-150 is a 6 1/2' bed the F-250 is a 6 3/4' bed. Long beds I think are the same 8' for both. Also a F-150 supercrew has 5 1/2' bed and a crew cab F-250 has a 6 3/4' bed. I don't know about the width, but I would assume the are a little wider, I don't have the specs at hand though.