EgoDeath

Hey everyone I'm stuck and need some help, I have an 05 base model Z w 116k miles. Running short tube headers, CAI, and a catback exhaust. I've been having a loss of power but sometimes when I'm steadily accelerating, the power comes back every now and then. My mpg has been terrible. The idle is not bad it usually stays at around 700-1000 rpms. The only codes I've been having are P0171 & P0037. When I reset the ECU by disconnecting the battery overnight the car ran perfectly fine with good mpg but after 2 days it went back to running lean. I've checked for vacuum leaks with brake cleaner but haven't found any or heard any hissing noises from the engine bay. I've also replaced the rear O2 sensor after the cat and am still getting the P0037 code, also the old O2 sensor was black and had a lot of carbon buildup. I have a feeling it's the cats, they're really old and rusty but I'm not too sure. The next thing I might do is clean the MAF but I'm not sure it's that because I can see the live data reading & it's ok. I'm just not sure what could be the cause of running lean on bank 1. If anyone could help me I would greatly appreciate it.

EgoDeath

Update: I cleaned the MAF and the TB and the lean code went away for an hour. I continued driving it but it still felt like it was running lean. When I'd start from a stop I would feel slower than usual then at higher rpms the car would regain the power. :/