1999 Silverado 4x4 with 6.0

I have a 1999 Silverado that I have not been driving that much (since October 2013). One of the last times that I drove it it started to run a bit rough, it back fired and farted a bit,
then I parked it and only drove it a few times for maybe six miles each time. No back firing, but it was still running a bit rough.
It is about time to change the fuel filter on it, again, and put in some good fuel before I do anything else.
Anyway, a couple of years ago I replaced both post cat O2 sensors because of the thing coding out. Approx two months later the RB post cat sensor started coding again, but the truck ran fine and I foolishly just ignored the service engine light. Of course I could not find the receipt to exchange the part (found the LB receipt LOL!), and at 110 dollars I was not going to dump the money on it due to other circumstances that have changed into other circumstances.
To put it plainly, I cannot afford to dump $110 on the truck at the moment. I am wondering if the truck was sensing a rich mixture and leaned out the RB too much. If this is the case, is there a way to parallel the LB sensor temporarily? I suspect I can mess with the connectors to make sure that they are making good contact. Both replacement sensors were Bosch and had factory pigtails. I cut off the old sensor pigtails and might be able to fab something together without hacking into the truck wiring.
I just hope that the cat wasn't fried. The truck did smell like it was running hot in some fashion. I might have cooked the thing off.
I figure that if I run the sensor in parallel it will at least give the right bank a close approximation of the proper mixture to dial into the RB.
(not proof read or spell checked - sorry)
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