Re: Lincoln 2003 Acceleration
100K miles? It might be due for tune up #2! More so new plugs. If the truck went in for a 60K service, chances are good that the dealership used copper core plugs, which are good, as they're my choice, but they should be replaced every 30-40K depending on how you drive.
Also, with 100K, you might want to consider a transmission service as well (not a flush), and a 4x4 service as old dirty oil can add drag. If you drive in overdrive at 80-100km/h the engine isn't turning over much either, say 1500-1700rpm depending on your speed and axle gearing, so if you have a decent load on board, the transmission will lug some until it decides to downshift or you put the go pedal down a bit.
Another thing to try first, is to put the transmission in 3rd gear, and drive it at the same speeds on a local rural road for five minutes or so. Engine speed will be in the 2500rpm range (or so) and that will rule out any engine lug, and if the engine gets very raspy or sounds different than normal, then I advise a tuneup..
'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!