After installing a 4" lift I had the usual vibration in the rear driveline so I dropped the tcase using the stock spacers. The rear driveline vibration went away but now, when I reverse I can feel a strong vibration on the on the other side of the firewall near the accelerator. Happens at around 1400-1500 rpm but GOES AWAY when I step on the brake pedal while holding the accelerator steady. I had my friend check if the brake booster was vibrating or if the air pump line was hitting the firewall but it wasn't. Anybody experience something like this after dropping the tcase 1"?? What did you do to fix it??