GMC Repair: 1999GMCSubruban K2500 Exhaust, ca emissions, o2 sensors

Question
Suburban is 1999 K2500 Suburban with 7.4Litre engine 4WD, AC,PS,PB,AC, with 108K miles.  The fuel pump was replaced, at 102K miles truck runs fine until 107K then Service Engine Soon light comes on, code indicates cats are blocked.  Since then we have replaced exhaust/cats 3 times, MagnaFlow exhaust, along with O2 sensors as Service Engine Soon light keeps coming on after about 125 miles.
Took truck back to local dealership in TX, asking to have computer re-programmed, they refused and are now telling me that because this is CA emissions Suburban, I have to live with the light being on, or spend $1500+ for CA emissions exhaust.
Please help


Answer
Hi
Do you know what the codes are?? P0420 and or p0430?
Those are Low effiency codes.
Please let me know this...
In the mean time...
I have run into aftermarket cats not being up to OEM standards.
After the 125 miles, are the codes the same everytime?
If so are they the Converter effeincy codes?
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Thanks
Pawl