[MASTERBrian]

I have a 2012 Yukon xl Denali with 88,000 miles. Normal driving it seems the transmission runs in the 130's most of the time, for fun let's say 120-150 range.

When I look online normal transmission temps seem to say 175-195 is normal. Things also seem to say cooler is better and my temps seem to be about par for course. Not worried there and this obviously had a trans cooler with the Denali package. Online reading seems to say over 220 varnish starts forming.

This past weekend we made a trip to Colorado and drove past way up Pikes Peak. It was only open 13 of the 18? miles, which if familiar is at the brake checkpoint when coming down. On the way up I decided to check trans temp and saw it was at 195 and climbing as we got to about mile 9. Around mile 10/11, it was into 205/210 range, so I'd pull over let the numbers drop a bit then continue. Of course the higher I got, the more it climbed and thus I'd pull over a few minutes to let it cool some then continue. Highest reading I got was about 217/218 and that wasn't for long.

Once we got to the 13 mile section we went into the gift shop area for 15 min or so before going back down as the upper part was closed due to storm moving in. On the downhill I ran in 1st most of the time with the occasional shift into 2nd for the flatter and longer stretches. Temps came down fast the lower I got, but I thought odd it would drop faster in 1st, raise up a bit in 2nd. In 1st I'd run about 2-3000rpms, in 2nd about 1500-2000rpms. Problem is on steep parts in 2nd required lots of braking, so 1st was the place to be.

I guess my question is, is that normal for the trans to get that hot doing a drive like that? I do realize steep climbs, with lots of switch backs isn't easy on anything and Pikes is a 14er, but I was shocked the trans got that much hotter than normal that soon....I question if I could have kept her cool going to the summit, without stopping for long periods several times to cool her down. I've made that drive many times over the years and never recall an issue in my other suburbans. I think I took our 92 2 wheel drive and our 99 k1500 up that we had and I know I've driven our 2003 2 wheel drive up several times.... of course no trans gauge on them so maybe unaware of temps they reached. Hmmm!! I'd think this 2012 would be the most competent.

The other part I found interesting was that the transmission cooled faster in 1st gear going down than 2nd, in which temp would jump about 5 degrees when I'd shift to 2nd. Was it pumping the fluid through the colder faster in the lower gear? I'd think it would work harder in the lower gear!? Going up I just left in D, should I have chosen a lower gear for the climb as well? I did test trailer/haul mode some, but that didn't seem to affect anything.

Just looking for some insight on this.....