1990 k5 blazer TBI help

[cst 72 blazer]

i have had the worst luck with the old tbi motors i would love to rip it out and go to a carb lol but besides that i want to stay with how it came.now my blazer idles great runs pretty good but has a slight miss at strange RPMs .it throws the check eng light once in a while and says the O2 sensor in pipe is getting a "lean" reading?> open to any good suggestions? im kind of thinking weak fule pump?thank you