I think a whirring sound is different than a hissing sound....

 

Do you have an HO? I might be off base here, but it seems like the J (HO) motors shake a little more then the N motors. I could be wrong.

 

how do i find out

 

VIN number. The 8th digit tells the engine, I believe "N" is the regular 4.7 and "J" is the H.O., that might be backwards....

 

You are correct

 

My non H.O. shakes a good amount. I run 93 octane on a 91 performance tune, a clean throttle body, sea foam through the engine, colder plugs, new MAP sensor and it still shakes as much as the day I got it. The previous owner said the truck has done it since day one because my dad questioned the wierd shake. He didnt want it to turn out being the injectors. Ive had the truck for 25k miles where I have drove it like I stole it, and it hasnt got any worse nor any better with anything Ive done.

If you do have a H.O. motor, a few members have found their shake to go away by using a premium octane fuel. The manual states you can run either, but the premium will help this issue.
If you dont have a H.O. motor, and you dont have a tuner I wouldnt recommend a premium octane fuel. It actually turns out that the high octane will hurt the performance of the motor.

The first time I changed my plugs, it was at 100k miles (no idea if the prev owner ever touched them), and I pulled out 8 copper core champions. None of them had anti-sieze on them which was pretty scary, and the plugs near the rear of the engine had no electrodes left. I couldnt believe the cylinders were still firing since the gaps were over .1, but the new plugs didnt really help it run any better. It never ran bad though.

 

I have the HO and run Premium. Mine idles pretty smooth. I'll get a slight shake on hot days.

 

did this do anything at all?

 

Ah, nothing that I noticed. I didnt dump to much in there as Im not too wild about additives. Ill probably run some through before I install my catch can to clean up any oil in the intake.

 

yeah i was checking out the website and the video shows them pouring the stuff right into the PCV hose with the engine running and to "be careful" because pouring too much in at once can hydrolock the motor....dangerous stuff in the wrong hands if you ask me...i just wonder if it's one of those "mystery" additives that really does nothing....