Service Engine Soon Codes.Please Help!

I have a '99 Tahoe that is having some O2 problems I believe. Let me start from the beginning. My wife and I took it to have new brakes put on at Midas. While it was there, I had them replace the exhaust donut gasket on the drivers side since I knew it had a leak. Well, about ten miles into our trip home the service engine soon light comes on. When I hooked my code reader to it I get codes P1133 and P1153 which I believe are seperate O2 codes. My first thoughts were since they had the exhaust apart maybe something came loose. Got under the truck and couldnt find any loose connections or anything really. So, I thought maybe it was just a blip since they were messin with the exhaust so I just reset the light clearing the codes. And also during this time I have not noticed the truck using any more fuel than normal or the engine running funny--nothing out of the ordinary...just the light on the dash. So after resetting the light Ive driven it now for nearly a week and thought that the problem had went but today the light reappeared and when I checked it was the same two codes. If it were just one code I would just go get the part and replace it, but two seperate sensors at the same time? Seems more to it. There is no change in the way it runs or accelerates or anything. So anybody with any info would be very welcomed. Thank you

Make sure that sensor is plugged in properly bank 1 sensor 1. l/s before cat

i'm having the exact same problem. donut was replaced, then service light came on. was reset, then came on again. i also looked for any loose connections, but didn't see anything. was just going to replace the sensors, but wasn't sure which to replace - the front or rear. will probably start with the front after i verify the bank/sensor plug-in from the previous comment. will let ya know if i get it fixed!