I have an 03 tahoe thats almost at 300,000 miles. Original tranny lost the 3-4 clutchpack at like ~230,000, Im pretty sure even the spark plugs have never been changed.
Oh and I did one front wheel bearing at like 250k, an ABS module at 100k, shocks at 250k, driver side heated seat element at 150k, driver side window regulator at 200k, and a transfer case encoder motor at 225k. But other than that its 99% original as it came from the factory. Other than the driver side window regulator and heated seat element Ive had no problems with the interior, no HVAC problems or anything.
5.3 still runs like new and screams when I hammer on it, still has 40psi hot oil pressure at idle, etc.
Gets an solid 16mpg, but I dont try to drive it for fuel economy either.
The only thing is I think the front diff is starting to get a little worn, because it kinda whines a bit when the front axle is engaged (ie, when its in Auto4wd or 4high). But honestly, for 300k I couldnt ask for more reliability from it. The GMT-800 tahoes/suburbans are all around very solid reliable vehicles and will last a long time.
ben