I have a 2002 Suburban LT with 315K on the odometer. At Idle while in gear, it bucks for lack of a better term. I have changed plugs, wires, coil packs, O2 sensors. It does throw a random misfire code and also bank 1 lean code. I can clear the codes and it still bucks ONLY at idle in gear.

 

check your fuel pressure with the key on and engine off and then when its idling should be around 55 but no lower than 51