Hello all, I am new to this forum and have a few questions on my 2004 GMC 2500HD crew cab. 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

 

I bought the Spectre cold air intake from autoanything. It is very well made the weld are very nice and clean. I was glad to save the extra $100 bucks. It made a difference in a few different ways. I really did not notice any fuel improvement, but at the same time i put on a agnaflow and my foot always puts the pedal down just to hear the sound.

 

It looks like your truck needs 87
Powertrain / Chassis Vortec 4300
4.3L V-6 (LU3) Vortec 4800
4.8L V-8 (LR4) Vortec 5300
5.3L V-8 (LM7) Vortec 6000
6.0L V-8 (LQ4) Type 4.3L V-6 4.8L V-8 5.3L V-8 6.0L V-8 Displacement (cu in / cc) 262 / 4293 294 / 4807 327 / 5328 364 / 5967 Bore & stroke (in / mm) 4 x 3.48 / 101.6 x 88.4 3.78 x 3.27 / 96 x 83 3.78 x 3.62 / 96 x 92 4 x 3.62 / 101.6 x 92 Block material cast iron cast iron cast iron cast iron Cylinder head material cast iron cast aluminum cast aluminum cast aluminum Valvetrain OHV OHV OHV OHV Ignition system direct composite distributor, platinum-tipped spark plugs, low-resistance spark plug wires coil-near-plug, platinum-tipped spark plugs, low-resistance spark plug wires coil-near-plug, platinum-tipped spark plugs, low-resistance spark plug wires coil-near-plug, platinum-tipped spark plugs, low-resistance spark plug wires Fuel delivery sequential fuel injection sequential fuel injection sequential fuel injection sequential fuel injection Compression ratio 9.2:1 9.5:1 9.5:1 9.4:1 Horsepower (hp / kw @ rpm) 200 / 149 @ 4600 285 / 212 @ 5200 295 / 220 @ 5200 325 / 242 @ 4400 Torque (lb-ft / Nm @ rpm) 260 / 353 @ 2800 295 / 400 @ 4000 330 / 447 @ 4000 365 / 495 @ 4000 Recommended fuel 87 octane 87 octane 87 octane 87 octane Maximum engine speed (rpm) Manual 5600 5600 5600 5600 Maximum engine speed (rpm) Automatic 5600 5900 5900 5600 Emissions controls 3-way catalytic converter, exhaust gas recirculation, positive crankcase ventilation, evaporative collection system 3-way catalytic converter, exhaust gas recirculation, positive crankcase ventilation, evaporative collection system 3-way catalytic converter, exhaust gas recirculation, positive crankcase ventilation, evaporative collection system 3-way catalytic converter, exhaust gas recirculation, positive crankcase ventilation, evaporative collection system
I do not think the XM and Sirius are hardware compatible, look in your owners manual it will explain the XM radio, as for the tires you may loose a little torque, but you may gain a little fuel mpg. Larger tires will lower your gear ratio.

Enjoy your new truck
vp