I have the 2.5" TGC and I do have the 4x4 shudder. That is when it's in 4x4 mode and you accelerate there is a bad shudder (in a straight line for testing - don't drive around on the street in 4x4 mode unless it's an AWD model) It's not there stock. Seems a lot more common for us with the 2.5" spacer. From what I've read here on DT it's because the CV joint on the front axle is at too sharp an angle and it's binding up. At some point I'm going to pull my 2.5 and go another route.