HI, any input would be greatly appreciated. I have a 99 grand prix gt stock .. my gas mileage has not been as good as the last 99 grand prix. car has 78k miles on it.i decided to change out the o2 sensers to see it it would help as it did on my old one. got bosh sensors and started getting p1133.took them back and changed them and again intermittent p1133. took them back and put in ac delco and still getting intermittent p1133. checked all wiring. heater circuit seems to be working with no voltage drop. switching circuit bounces from 200-800 mv as it should. started scanning with hpt and found a lot of kr at 80%-wot. at wot o2 hangs steady at 850mv. i found some corroded terminals on the coil packs on #1 & #3 so i replaced all 3 coil packs, plugs and delco wires. no change in the kr. put in 10 gal of 93 octane and my kr seems a little better. kr would go as high as 8 and with the better gas not going over 4 much. do i have a fuel problem? I am stumped on the p1133. should i just turn off that dtc with hpt? I want to figure this out on my own so i can learn but im stumped. Thanks, and sorry if i posted in the wrong section.