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So I finally gave up on waiting for a fix for the 8 speed and its many mis-behaviors and had my truck tuned by a local custom tuner that has been working with LS/LT motors and transmission tuning for many years. He plugged in his laptop and rode with me for over two hours. The truck is a new animal. Great at shifting and the engine acts like the beast it should be. My truck is a 2015, 6.2L 8 Speed, 23,000 miles. It has always had the low speed clunk and recently developed the shudder, especially in 8th at steady state highway speeds. Here is some of what was done. AFM shut off, Torque Management shut off, Variable cam timing adjusted to performance lift, 1st gear set to hold until 11 mph, higher shift pressure for next few gears, torque converter set to 0% slip, raised speeds for converter lockup especially in 8th. Other parameters were adjusted, but these were the main ones. Some of what was learned. The TC was slipping too much when trying to lock at light load (half in half out) causing the shudder. It was also trying to lock at too low of a speed/RPM almost lugging the engine (again most pronounced in 8th). No more shudder in any gear. It does take a decent speed (over 60-65 to lock up in 8th, but once locked it will stay locked below 60 unless I kick it in the pants or the load increases). As most of you experience, 1st gear was trying to get to third as quickly as possible. Now I can move through parking lots without trying to throw a U joint. There were more learnings but these 2 are the big ones. I will probably lose a bit of MPG in town driving (I am fine with that) but the 60 mile trip home at freeway speeds netted 20.1 MPG ... not enough loss to consider if any. Performance is incredible. I floored it from a stop a couple days later, and had to back off to preserve the tires as it started roasting them. Shifting at full throttle was impeccable. Longevity (as long as I dont drive it live a sports car) theoretically will be better than it was with all the clunks and shudders. I am thrilled with the results. If any of you live near Van Buren Arkansas, and are interested I will pass on the contact info.
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I bought this truck in August of 2014 from a dealer in Milwaukee. It had 8k miles and the previous owner had custom ordered it used it for 6 months then turned around and traded it in for same thing but 2500 with a Duramax. This is its journey.... The truck also did really impressive burnouts for being completely stock, this one was into 3rd gear A few months after I bought it I started with upgrades. First was a rolling tonneau cover. Didn’t love it but it worked. I wanted more power from it and chose a set of Doug Thorley tri-y headers and catless y pipe. Had a little issue with y pipe not being the right size for 6.2s catback, welded factory flange onto the y pipe and it works great! Plus they look sweet! At the same time as this I also bought a Diablo inTune, it paired alright with the headers but didn’t have the parameters in it to tune out cats so I had to have someone do that for me. The truck did have some pretty amazing fuel economy though. This tank was hand calculated 24.5!! I drove the truck like this for a couple years but did a few minor things, one was an MIT tube and the other a custom tune from DiabLew. Trans tuning was biggest improvement by Lew.