According to the Motorhome Magazine
Towing Guide, the '04 F-150 4X4 should be towable 4 down. HERE
is a link to the Motorhome Magazine
page. The towing guides are toward the bottom right. Check you owner's manual for the F-150. There should be a section on recreational vehicle towing.
If the towing guide is correct and the '04 F-150 is towable, the only problem I see is weight. A 4x4 F-150, especially if it is an extended cab, will run close to 5000 lb. with gas, water, "stuff", etc. on board. I see by your signature you have a 34' Sightseer motorhome. It is probably on a 22,000 lb. GVWR chassis with a GCVRW of 26,000 lb. That means if the motorhome is anywhere near fully loaded, you only have capacity for a 4,000 lb. toad. Also, the hitch on the back of the motorhome is probably only rated for 5,000 lb.
Unfortunately the Motorhome Magazine
web page doesn't go back to '99. For the Towing Guides they do have I see the Blazer (based on the S-10) is towable, but the S-10 itself is not. Maybe someone else can help with the '99 S-10.