2007 Denali bought used with 69K miles, and currently has 75K miles. 6.2L motor.
Should I have the tranny flushed, drain and fill, or leave it alone?
I've read different stories about flushing, but I don't have any clue as to what the previous owner has done to the vehicle, so maybe it's just for my sense of security.

 

Yes, absolutely. Take it to your dealership and have them do a servicing of the transmission. Do a transmission service about every 50,000 km or 30,000 miles. Change the fluid and the filter. In Canada, where I live it costs about $150 to complete the service.

With no prior knowledge about service history on the vehicle, you have to assume that any servicing was minimal.

 

As long as the fluid does not smell burnt (it should not at that mileage) have it flushed.

 

Thanks guys, I'll get it taken care of.

 

Change automatic transmission fluid and filter if the
vehicle is mainly driven under one or more of these
conditions:
− In heavy city traffic where the outside temperature
regularly reaches 90°F (32°C) or higher.
− In hilly or mountainous terrain.
− When doing frequent trailer towing.
− Uses such as found in taxi, police, or delivery
service

50,000 for 'severe' service, and 100k for 'normal'

I bought mine new, it has 30k on it now... it won't get it till 100.

I tow a 5,000 boat with electric brakes exactly 1.2 miles to and 1.2 from the launch every few weeks in the summer. No major hills, no major traffic...

 

You do that and the thing wont last past 100K. I use a different schedule. Change tranny filter and fluid every 10,000 miles if you are in the Heavy Duty Schedule(A). Otherwise, tranny filter and fluid replacement every 30,000 miles under normal use. Thats how you take care of stuff and can get close to 200K in one unit.

 

The owners manual for this vehicle says for the 50k/100k mile maintenance plan to change the Automatic Transmission Fluid and Filter for the severe service and 100k miles for this maintenance for the normal service plans. This information is found on page 554 of the Owners Manual. I hope this information helps you.

Jeff Morris, Chevrolet Customer Service

 

dude, we live in 2011 Just relax and let trany do his work and don't tread it like kid
My tranny died in 60k but car was under 100k warranty Now i have brand new with another 100k