2000 gmc z71 5.3 o2 sensor code

codecomes out bank 1 sensor 2. changed sensor switched it around no luck. same bank and sensor code. checked for vaccume leak with carb cleaner and hose in ear, no luck. truck has loss of power a sputters at take off. no backfire. if u turn off ignition aand turn it back on problem may stop for several minutes to several days.truck has no cats.