Truck seems slugish...

[gordo]

what did you gap the spark pluggs to? the previus gap or did u leave the .40 gap that the delcos come with. I just did a tune up on my friend new denali, it 2 was sluggish but we cleaned the throttle body and changed the pluggs with the right gap and the issue was fixed

 

[mhorn0817]

i just put them in out of the box. i thought they came pre-gapped

 

[Ironman1979]

nope.. i just got a set of plugs for my truck and out of the box they had gaps rainging form .025 to .050.. gap on my truck is supposed to be .035

 

[sparg93]

The AC Delco premium plugs (i.e. Iridium) do come pregapped...it is recommended however that you check each one prior to install just in case one or more is off.

I just did my tuneup and they were all spot on...but unfortunately it doesn't mean yours
were as accurate.

I'm not sure if your '04 was part of the change, but there was one or more years in the NBS that came out of the factory with one gap settng (i think it was .06) and then GM came out with a release that the truck will run better at .045. I have an OBS so i didn't track the change, but it might be worth investigating for the appropriate changes and then pulling one or all of your plugs to check gap.

However, I would bet those 20's are a bit heavier then what you had and rolling mass can make a difference in accelerating. I would recommend going onto sites that sell the rims/tires you have had and adding up the weights.

 

[Sasquatch]

When i swapped from my stock 16`s 20 inch LTZ wheels i weighed them both.

The stockers were around 71 pounds and the 20`s were 92 pounds. The weight is for one tire and wheel.

With the increased weight and diameter and my yukon having 3:42 gears i felt a difference in off the line acceleration and a slight difference in braking.

 

[01HDtahoeNJN]

Seafoam, plugs/&wires.... Clean tb and replace fuel filter???no expert whatsoever but may help with process of elimination