Transmission-rebuilt?
4 months ago I bought a 1998 Suburban-2wd-(about the same drivetrain etc as the Yukon, but 14" longer)with 196000 miles(300,000 km) on it.It has been prefect in the last 2000 km. However-144,000 miles is about when you can expect the transmission to need a rebuild.A rebuild/reinstallation is about $2300 here in the USA-1500 Euros.
If you are handy and game you can buy a new-not rebuilt OEM trans from GM for about 1000 Euros.The duties,and shipping will be extra, of course(I sent a motorcycle head to France for fancy porting,and ended up with 25% duties on the very inflated worth of the head-I exaggerated and said it was worth $500 when it was worth more like $50-BIG MISTAKE).
Check to see if a trans rebuild was recently done. The AC compressor usual dies about that time also.The motor can still be nice and tight at 140,000 miles.Eyeball the dipstick;I've noticed that ones that had frequent oil changes and checks don't have a build up of crud above or below the oil level line.
Listen carefully for engine noise.Items attached to the engine might rattle-no big deal-but the engine itself should be nice and quiet with no odd noises.
The electrical gadgets-power windows/mirrors/radios can be surprisingly durable, but check everything.Having a power window motor replaced will be several hundred $$.
Luck,
Charlie
PS I get 13+ mpg in mainly city driving with about 40% in city expressways.Pure city stoplight to stoplight-with careful driving-gets about 10-12 mpg.