Fix-engine vibration just above idle

My 2003 Silverado xcab with the 4.8 vibrated when accelerating from a stop. The vibration was disconcerting especially taking into consideration the reputation for smoothness the small block has. The vibration occurred just above idle and was gone above 1000 rpms. I almost felt like a plug or coil was misfiring. This was very bothersome as I am past my hotrodding days and accelerate at low throttle. This kept me in the vibration range longer. Took it to the dealer. They mentioned several service notices and installed a factory supplied flex coupling just ahead of the muffler. This solved the problem. It is nice to have problems solved. Hope this helps someone. BPILOT