Just bought a used 2001 has a couple of issues. 1) fuel gauge in op. checked bad sensor waiting to burn gas out to drop tank. 2) clutch needs to be bleed or adjusted, hard shifting. Working on that. 3) It has a hesitation or stutter when in neutral . If I rev up it kind of hesitates and a little sputter or vibration and when it first revs up sounds like a vacuum leak for a second or two then smooths out. Installed new plugs , no help. Put some injector cleaner in but have not driven enough yet. I suspect the hesitation and what sounds like a vacuum leak are connected. I have another F150 a 2008 and it runs perfect. both are 5 speed. Both 4.2 V6.
The plugs were worn on a couple cyl. no codes.