Time for a tranny service

[mishalah]

2004 Denali XL with 78,800 miles. I've had it since July '12, and when I changed the oil immediately after buying it (74,700 miles) it was low and filthy. All the fluids were checked/topped, and I had to rebuild the front drive diff and replace a cracked axle tube shortly thereafter. Everything has been fine since, except for some coolant spewing out mysteriously every once in a while......AND slightly more than a qt. of ATF just disappearing about a week or two ago.

It was shifting a little jerky so I checked the fluid and found it just barely on the stick. Quite a surprise since I check it every month or so (only 4000 miles since July), and I've never seen a drop on the ground. Anyway, since I have no idea if the last owner ever changed it or the filter I figure I'll get it done.

The big question is: flush?.....or do the standard filter and partial change? The fluid is pink and clean looking at this time. I see opinions about flushing all over the map here and other places....so what do tranny experts really say? What does the GM dealer say? What does the tranny maker say?

[maxwedge]

GM does not recommend the use of a flushing machine, also use Dexron VI, more expensive but it is superior to Dex111.

[mishalah]

Originally Posted by maxwedge

GM does not recommend the use of a flushing machine, also use Dexron VI, more expensive but it is superior to Dex111.

I did a full fluid and filter change (pumped it out through the tranny cooler lines)at 92,000 miles in my '05 Suburban -- from Dex III to Dex VI. It's a lot of work because all the Dex III has to come out. Coincidentally or not, I started having shifting issues not too long after (all at about 100,000 miles). I replaced several selenoids, the TCC harness, and finally the $1350 ECU before it got straightend out. I don't know what exactly caused the whole problem, but it was a nightmare. I'm gonna leave the Dex III in this one until I know for sure there won't be any future consequences....even though the Dex VI is MUCH better fluid.

These trannies are waaaaay to sensitive for this day and age.