Picked up a 2014 gmc 1500 with a 5.3 and 6l80 last summer with 195k. Put about 7 k on it before the transmission went out. Just started slipping and replaced it before it left me stranded. Replaced with a new-used one ( I am aware that’s a bad idea but all I could afford). Completely flushed trans and cooler with Napa service pro full synthetic fluid. Drove good for about 4,500 before it started to shudder ever so slightly. I immediately flushed the fluid again and put the lil lube guard shudder stop in. Drove good for about another 5k, then started shuddering awfully. I could make it stop by putting it into m5 or if the trans got hot, I could put it in m4 and it would stop. Decided to put a new OEM convertor in. Just finished that, completely flushed the entire system, prefilled the converter and overall put 10.5 qts of Service pro trans fluid in again. Immediately started shuddering again as soon as the trans got north of 100 degrees.

Im stuck on how a new torque converter and fluid didn’t fix it even for a little bit if last time just flushing the fluid fixed it. Anyone know what else could cause the “rumble strip” like shudder that only happens under light loads and low rpm from 45-65 mph.

thanks in advance!

 

binding or imbalance in the rest of the driveline

 

I thought it might be that, but it only does it when the transmission is warm, and the first time it happened I fixed it by changing and flushing the fluid.

 

maybe the flex plate is warped?