2002 w3500 left bank of injectors malfunctioning

[ericrlong]

I have a 2002 gmc w3500 with a 5.7l v8. and 29,000 miles. vehicle suddenly started running very poorly. replaced all spark plugs, wires, rotor & cap. notice all plugs on cylinders 1,3,5 and 7 were heavily sooted while the plugs on right side were burning normally. Took the vehicle to gmc dealer and was told that the left side injectors needed replacement and was not covered under my 5year-50,000 emissions warranty. $1,000 to replace 4 injectors. They said this was caused by a dirty fuel filter. My thought was "hogwash". First of all it should be under my emissions warranty. Secondly, how could a dirty fuel filter cause injector failure on only the left bank? My limited knowledge of this injection system tells me that there is a component(s) that triggers the left and right banks of injectors. I would appreciate any input so the issue is handled properly.