Advice for a potential tuner

Hello everyone, first post! I need some guidance, input on whether to purchase HPT for transmission tuning on a 2015 Sierra Denali 6.2 8sd. I bought the truck knowing of trans issues, but didn't know the hard downshifts were so bad...I was in a coasting situation about 30mph, gave gas to pass, hesitation, then it downshifted hard, like there should have been trans fluid on the road. This super hard downshift is rare, most of the time I get a double clunk and go on. I've done a new trans filter and new blue label fluid job, not much help.

My question...Can the HPT or any other tuner help the 8L90 trans with shifting issues? I've been reading and youtubing all I can, seeing how changing mph numbers in upshift and downshift could help. I don't mind investing in a tuner, and putting is the time to learn how to use it correctly, but I would like to know if there is light at the end of the tunnel. Would like to keep the truck, but trading off is my other option. I've done the "D" tuner, firm shifts not any help, 87 octane canned tune, AFM off, about all from it.

Thanks for your time, look forward to hearing your input,
Alan

Has the transmission had the new Mobil 1 fluid installed in it yet??

There is a new fluid for the 8 speed transmission that does help with some aspects of the transmission. A reset of the adaptive learning would be a good idea too.

It does have the Mobil 1 blue label fluid, a reset of the adaptive learning has not been done. I will put that on my list to do.

Log/watch your trans fluid temp. I'm a driveline tech at a Chevy dealership. We do a lot of 8 speed trans harnesses. The temp sensor is built into the harness. It's a split 2 piece harness. You will need the one with all the solenoid connections. The sensor is an updated part. These 8 speeds will do crazy stuff when the temp is fluctuating. Seems like the temp controls shifting more than MAF or torque does at times. Graph the trans fluid temp and look for abnormal spikes and drops. It should stay pretty steady and build accordingly with operation. I just did one yesterday. I'll see if I can find the old part and post a picture. I think the 2018s got the update but anything older will need it at some point.

Good information, I haven't ran across this in my reading, I will look into the trans temp!

Yea I haven't read it much online either, but I can tell you that the other tranny guy an I do about 1-2 a week on 14 and up trucks with 8 speed. When they get really bad a P0711 will set in tcm. It really screws things up when you are trying to do the fast learn and it drops out of the required temp range. Locks the trans in neutral sometimes. Have to reset the vehicle by removing battery cable

Got the HP tuner up and running, wish I had known of this tuner before I got the diablo...oh well. I've been doing some data gathering, and watching the trans temp, not seeing anything weird, seems steady, no code yet.

I've been reading up on the adaptive learn reset. I need the trans temp at 165, click trans adapt reset, click trans adapt presets, and then trans fast learn, put in D and apply brakes the entire time, sound right?

Having a good time learning how to use it, just going through basics, I'm an old noob!

On the 6 speeds I never click trans fast learn. I just open the scanner and connect to the vehicle with the key in the on position, click adapt reset and then preset and start the vehicle. I don't even need the vehicle at temp to do that either.

Yes on 8 speeds trans temp needs to be between 167 f and 185f if it falls outside of the range it will fail and lock itself into neutral until the module is reset. 6 speeds there is just a push of a button to reset adapt at any time.

thanks for everyone's input, trans got better then bad again after doing a reset, much worse, I did another reset then traded it!