Hesitation problems
 

Hi I have 2007 Lincoln navigator L 1000k*
I have a hesitation problem. This are the symptoms > when I use premium gasoline, the car skips/hesitates on the highway at over 2500rpm.*
When I use unleaded gasoline, the hesitation occurs at any speed!*
I got a p308 code. Changed the coil and the plug on #8, plus changed fuel filter and air filter. The car still runs the same :((
Pls help. Eric.*

try seafoam and run it real hard wont hurt :-X06

Update! Changed all the plugs today, drove it for about 100 mi, the problem/hesitation seems to have gone away! Drives really nice :)
5.4T thnx for the reply. I tried A few fuel additives. I only had about 60k on the old plugs, so I didn't expect the plugs :(