Yeah, that's my hypothesis. Though, it seemed to take a while, and I did a couple other things (went back to a 187F Thermostat from the 180F), fixed what appeared to be a leak or two....
That said, I agree, the OP should try the Denso 234-4668 sensors and if it works (may take a little while to work) then we can jot it down as a potential solver of the P1133/1153 problem via better O2 sensor quality.
'09 PSM G8 GT - OPG Intake, DOD-Delete w/ Stage 1C 218/229 .600 Lift 117.5LSA, Kooks 1 7/8 Mids, Solo Axle-Back w/ X-Pipe, SuperPro Bushings (Front and Rear). BMR Sway Bars (Red)
"If you want to criticize someone else's work, be sure that your own is in order first."