Rep Power: 0

Hello, I have a 1994 DX 1.5L 16v with 172K on it. About a year ago I did a head gasket and a valve job to the head. I have also replaced the O2 sensor. I removed the AC belt as well. The car has consistently gotten 34-36mpg. In october I had to replace the exhaust. When I did, I decided to hollow out the cat, hoping it might improve the gas mileage. Right around the same time I noticed at higher rpms my battery light was coming on. I assumed it was a slipping altenator belt. I readjusted it, but still had the problem. I assume its probably the altenator now. Ever since october I have noticed my gas mileage has decresed to 30MPG. Does this make any sense?