GMC Sierra 6.2 vibration when towing up hills

[ArPix]

Greetings bitogers! My 2015 GMC Sierra 1500 has the infamous 8 speed automatic trans. The truck has the 6.2 liter engine and currently has 31K miles. Earlier this year I had the ATF and filter changed due to the trans shuddering. The shop used Mobil 1 blue label and added Lubegard Shudder Fix also. This eliminated the shudder but the lumpy shifting remained. We towed our 32' travel trailer to Oregon last week which included some mountains. We hadn't been able to use the trailer previously for two years. While towing up hill I noticed a vibration when the trans downshifted and the RPMs climbed. I don't recall there being this vibration two years ago when we made the same trip. So I am wondering if the new fluid and additive caused the vibration or has the transmission gone into a death spiral? Or something else?

 

[clinebarger]

Change it again with no additive, '15 would have the early fluid.

 

[ArPix]

Thank you Clinebarger. Should I use the Mobil 1? Would a pan drain and fill suffice or the dealer said they could do a fluid exchange?

 

[oil pan 4]

I would be worried the torque converter clutch was slipping but I would think it would go to maximum line pressure and throw a code.
I agree, dump it and no additive this time.

 

[clinebarger]

Thank you Clinebarger. Should I use the Mobil 1? Would a pan drain and fill suffice or the dealer said they could do a fluid exchange?

Mobil 1 Dexron HP "Blue Label", I would recommend a full exchange.