SDAT4

I had the same thing happen on mine at 75k (at 93k now) except I was towing a boat in 120 degree weather back from Lake Havasu. The new water pump I got from the Chevy dealer had an updated pulley design.

Just this morning when driving to work I noticed a whining sound then a few miles later when getting off the freeway it started having aggressive downshifts. Upshifting seemed okay but even when I manually downshifted it would jerk hard. I'm at 93k miles so of course out of warranty. Researching the forums, it looks like it could be a number of things including but not limited to: torque converter, valve body, idler gear bearing and torque converter. At 82k my truck developed the "rumble strip" vibration at highway speeds. I flushed the fluid and swapped a new filter myself which did fix that issue. I just don't think fluid/filter will fix this one. This is my daily driver that I also use to tow my toy hauler sometimes on the weekends (which it does great with). I really do not want to have my truck sitting for weeks or months diagnosing and waiting on parts like I've read on other posts. I'm thinking of finding a reputable shop here in San Diego north county area that has experience with the 10L80 or swapping a whole used transmission. I see them for around 2-3k on Car Part/junkyards. Thoughts?