2004 Gmc 2500hd Questions

[beerman07]

Hello all, I have a few questions on my 2004 GMC 2500HD crew cab that I just purchased. First, it has LT245/75R16 tires on it, after reading I found out that I can put LT265/75R16 tires on it, but will that improve or hurt my fuel mileage? Second, I found on craigslist a Spectre cold air intake for $75, is there really any difference between Spectre and K&N? Should I spend the extra money or go with Spectre? Third, I live in Colorado where we have 85 octane fuel, is it okay to run 85 with the 6.0 or should I run the 87? Lastly, there was a XM card in my glove box but I didn't see XM on the stereo, how do you know if you have it? Can I install my Sirius using the XM equipment?

Any help will be appreciated

Thanks

[txab]

Is there a satellite antenna on the roof? You should be able to check the RPO codes as well. Look for U2K I believe

 

Larger tire will hurt your mileage a bit

 

Remember your odo/speedo will be off due to tire size change. Your new tire is 1 inch larger dia. At 70mph you'll be about 2.7mph off. 70 = 72.7. So get your odo/speedo recalibrated.

[Stranger ranger]

Nothing wrong with the spectre intake. Filter might not be as good as others, but I dont drive in filthy environments so i really dont care.

[dewfpo]

85 octane at your altitude behaves the same as 87 at sea level so you are fine running 85 octane in your truck.

 

DEWFPO

[beerman07]

Thanks for all the help, much appreciated!