Look for a 5.4, especially if want to get that type of towing power.
Now I'm just assuming here, but if you have the money for an engine swap and/or rebuild, and a trade-in, you've got two days left of the Ford Family Plan. You could get an XLT 4-door, 5.4 liter for under 25K. You could pull away with a new truck. If payments are an option. Depending on your needs, you could go less $ for a 5.4 too with smaller trucks.
I'm in So Cal too and have talked to some Lightning owners that know mechanics who work on Ford engines. Where abouts are you and I'll try to direct you?