I have a 2004 GMC Yukon Denali with the 6.0l it started running ruff and has a severe lack of power the check engine light came on once it started getting worse p0300 (i believe that's it random misfire may be off a couple numbers) detected there is also a rattle in the exhaust that started just before i don't know if there related or its just coincidence that it rattles now that the engine is ruff and im just now hearing it since it stops when u rev it my main question is if it just needs a tune up wouldn't it know what cyl was misfiring

SOURCE: '04 GMC Yukon Denali Check Engine Light

Did u put in fuel shortly before the light came on? I own 2 service centers & the most common situation with "Check Engine" lights are because the fuel cap wasn't re-installed or not tightened. When you refuel make sure it "clicks" when putting back on. We don't charge for a "Code Reading" but a dealer will, don't go there. Go, like the others suggested. If it is the fuel cap & you re-install it correctly, the light will go off after a short drive. Good Luck. PS-Don't panic when the "Check Engine" light comes on unless it blinks, if that happens don't drive. PSS-RE: Murray's, Auto-Zone.......If it's a "Code" (the reader will give a #) the code book will tell you the problem. PSSS-Some1 please have Troy W's Mommy & Daddy take away his keyboard. Just because you can put together a "Lego" car doesn't make you a master mechanic. You only repeated what we said except you have a "Napoleon" complex against any1 plugging something in to a vehicle. It's the same as plugging in a light @ home. In conjunction with "kinder" nine out of ten time in my experience it usually is the oxygen sensor(s) which would be about right with the year model

SOURCE: Lack of smooth gear operation, rattling on front suspension over ruff surface

half shafts can cause a lot of problems with shifting and driving. but you could be loosing the third gear syncronizer.

SOURCE: check engine light 2004 GMC Yukon

When my check engine light went on, it was a oxygen sensor

SOURCE: rattling sound in steering (at low speeds)

I sounds like you need to grease the intermediate shaft. GM sells a kit that consists of a plug and a bag of grease for around $18. It has been a few years since I bought it so the price could have went up. They also offer an update shaft for around $100. I am nearly 100% sure this is your problem. I have a 03 Yukon and have done it 3 times in 120,000 miles.

There are a few other posibilities, but they are not so cheap. The next logical problem could be the power steering pump or the valve in the gear box.

SOURCE: 2002 yukon denali XL ac doesn't blow cold air.

You are going to need an a/c compressor, the clutches are gone.