I have a 96 grand caravan 3.3L engine and sometimes when cranking it in the morning it will start and then dies. I crank it again and it works fine then, but when driving ( mostly freeways ) at around 60 MPH the rpm's will drop drastically and then come back up again and the SES light will come on and then the van would stall. I checked the SES ligth codes and I came up with code 12 and 54.

Code 12 is the battery, I just replaced the battery about a week ago thinking it was the battery.

Code 54 is the camshaft sensor, but could this make the rpms drop so drastically. Please help me out and feel free to ask any other questions to have a more indepth description of the issue.