Hey, my 1989 Full Size Blazer went for an emissions test today. At first it was the usual dyno test but, the guy said because of my tire size the truck was not stable enough. So he did a different test. When I picked up my truck, whenever my foot is on the accelerator there is an incredible amount of shaking and vibration coming from the back of the truck. Any idea what to look for? Also, I have not done a gear change yet. I have a six inch lift with 37 inch tires.