When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
ROCKS is right - it's most likely the E4OD, but it might be the 4R70W. Either way, keep it cool (trans cooler esp if you tow) and change the fluid. If it's never been changed and it's over 60Kmi, I'd recommend changing it and then again 1000 miles later to flush everything out. Then you can go to a normal schedule like every 30-40Kmi.