Hey guys, I recently tuned my grand marquis myself with a SCT tuner. It did improve things, but it caused the car to vibrate in the rear end when tuned. It was only from stop to go, like when I was at a stop and pressed the gas. At high speeds it shifted kind of hard into second, but thats about it. I returned everything back to stock, and IT STILL VIBRATES FROM STOP TO GO. Everything shifts smoothly like it did before, but it is still vibrating in the rear end it feels like. Why is it doing this? Did my tune totally ruin my car?? I am eventually getting a tune from Marty at Mo's speed shop, but I just tried a custom tune done by myself and I fear I ruined my car. Please help
-1998 Grand Marquis LS
-Staggered Mustang Rims
-It's a mustang, but just overweight.