Re: 98 5.4L - E350 sparkplugs
13 years old, Id replace the plugs for better piece of mind regardless of the mileage. I'd also give the transmission a service as well. I'd also change out the rear axle fluid, or at the very least check the level and colour before you tow with it.
'00 Durango R/T 360ci 290hp (modded); 138,500m
'06 Pontiac G6 GT 3.5L 220hp; 44,000m
'12 Chrysler 200 Limited 3.6L 283hp; 13,000m
'99 Taurus 3.0L 2V Vulcan 145hp; 154,300m - Traded
Amsoil in all vehicles!