I'd be willing to bet that the dealer didn't put 5w20 in.
If you want to stick with a Xw20 oil, Mobil 1 0w20 will do fine. But I think Motorcraft, Pennzoil, Havoline, or Exxon 5w20 would do well too. The Pennzoil 5w20 comes in 5 qt jugs, BTW, and it's about $8 at Wal-Mart. Use that and change it at least every 5000 miles and you should be fine.