It is best to change the oil after every 6000 miles. The most important thing is to follow the recommendations for your car.
Every 2000 miles
You can buy a 2008 Chevy Tahoe at your local car dealership. They will often have older models due to various trade ins for the cars and other types of trucks as well.
Every 100,000 - change wires also.
If they are platinum plugs, should be every 95,000 to 100,000 miles.
It could be for many reasons. Since I haven't bought an OBDII scanner, yet, I take my Tahoe to an AutoZone. They will scan it for free and should be able to tell you the code number and what the problem is.
How often should you change the fuel filter?
Should change the filter at least 2 times a year. Remeber the fuel is always being pasted thru the filter. But if you get to it once a year that is better then not doing it.
Unless there is something wrong with it (there shouldn't be), you should never have to replace the timing chain. That's the beauty of chevy.
Follow the recommendations in your owners manual or change it every 5,000 miles.
as often as needed
every 10,000 miles
You should change your oil every 3,000 miles. If you drive your car rough, then you should change it more often.