looking for a good set of spark plugs that will last and get good mileage for 1999 E-150 5.4 What is everyone's thoughts

 

The vehicle manufacturer spends a lot of $$$ attempting to chose the best plugs for average use. There are some more expensive plugs that possibly will last longer and require lower voltage to produce good quality spark like Iridium plugs.
You might check different plug manufacturers and see what they offer that would satisfy your concerns.