oxigen sensor troubles
 

98 blazer LS 4 door 4.3L.
I have power loss, especially uphill, and I got some error codes about the oxigen sensors, so I bought new ones on eBay. No brand. They also gave errors, so the supplier sent me 2 new ones. Still error codes, and reduced power. So now I wonder, is there something else going on? Or are the cheap ebay sensors just categorically bad, even right after installing?

I got 6 error codes the last time:
p0171 FT System Lean B1
p1133 h02s insuficient switch ing b1 s1
p1153 h02s insuficient switch ing b2 s1
xxxx5 ho2s heater perfromance b1 s1
xxxx7 ho2s heater perfromance b1 s3
xxxx5 ho2s heater or slow performance b2 s1

I live in the tropics so I don´t worry too much about the heater.

Any ideas would be apreciated.