1998 e350 triton v8 seems to sputter when going up hill at highway speeds

An increase in load can cause a misfire when spark is not adequate or fuel pressure is low. Basically it has enough to run around town but when demand is high the engine can act up. You will need to start with basics like fuel pressure, spark plug condition and scanning for codes. Alex

Alex is right,and there are some test you can do to verify where the problem is. If you don't have the correct tools,then you can rent some of them at a parts store,AZ,ORLY,ADV, and when you take the rented tools back,you get all your money back that you paid to rent them.also,you might have to buy a couple things? copy and paste the link below,it is a test for the ignition coils (COP's) for your 5.4L engine. there are other test on this site that you can do also, testing other components.. easyautodiagnostics.com › Ford › 4.6L, 5.4L