2014 GMC Acadia shifting issues

I'm new here and can't find any info on how/or why my 2014 Acadia 3.6L trans is slipping on 2-3 and 3-4 after a long idle. No check engine lights I checked the oil was clean took it to the dealer 3 times they told me to change the trans oil and see if it clears the issue still nothing happened. On cold starts then drive off we're fine but after idling for about 10-20min it will start slipping 2-3 and 3-4. I have hp tuners and I messed with it a little, but I haven't been able to make any changes I have the stock tune stored on my laptop just in case and the tune I put into it. Would really appreciate it if someone can help me before I LS SWAP this thing lol.

The 6T70 in that vehicle has a common concern for a 2-3 flare in older models due to a weak 3-5-R wave plate that fractures and/or breaks. This issue was mostly corrected by a stronger wave plate design in the 2012 model year, however it should be noted that this issue can still occur. As for the 3-4 flare after getting hot is likely a worn 4-5-6 accumulator piston bore in the valve body. I had these issues occur slightly in my 2012 Impala (Same Trans model, but yours is a Gen 2 while mine is a Gen 1 - Hydraulic differences but same function) but I ended up fixing it by changing the clutch apply timing and the pressures on the affected clutches. The technical explanation behind the flaring is that one of the two clutches (it's likely the offgoing clutch) is not getting enough pressure so it is flaring. You can try to bump your offgoing pressure preset or your volume presets SLIGHTLY within your adaptive pressure functions to see if the issue resolves. Attached are my clutch apply changes. They are going to look different on the Acadia because of how GM calibrated it for the "good enough" feel of the shifts. First attacchment is Stock, second is my calibration. I have also attached my tune files for your reference. My calibration is HIGHLY modified so be careful if you decide to try anything, ESPECIALLY in the Shift Pressure presets. Attachment 117976Attachment 117977


Additionally, I have attached a link to a TSB from GM that includes your vehicle. This addresses a shudder in 1st and flaring shifts.
https://static.nhtsa.gov/odi/tsbs/20...83161-9999.pdf

GM Bulletin : 18-NA-358
Date of Publishing: Oct. 2020

Beautiful, I'm buying HP Tuners specifically to fix the wonky trans in my wifes 2007 GMC Acadia. It is not slipping but it has always felt mushy or to be one gear too high. Late down shifts going up hill and now has started to have an intermittent down shift then up shift jump feeling when under light throttle on flat ground. It only has 48,000 ish miles.