Gas Can I use regular 87 octane gas in a 2003 Ford F250 Supercab?

Here is the information from the owners guide page 232.

Octane recommendations
Your vehicle is designed to use
“Regular” unleaded gasoline with
pump (R+M)/2 octane rating of 87.
We do not recommend the use of
gasolines labeled as “Regular” that
are sold with octane ratings of 86 or lower in high altitude areas.
Do not be concerned if your engine sometimes knocks lightly. However, if
it knocks heavily under most driving conditions while you are using fuel
with the recommended octane rating, see your dealer or a qualified
service technician to prevent any engine damage.

Best way to check is by looking at the gas cap. If it does not say "Premium fuel only" you should be safe. Higher octane rated fuel is used for higher compression motors, and I dont belive that your engine (my guess is the 5.4 V8 should be around 9:1 compression) needs the high octane.