the codes i got out of my 1998 deville were: pcm - p0461,p0463, p0603
ipc b1552
Please tell me what these mean. Thanx

P0461 - Fuel Level Sensor Performance
P0463 - Fuel Level Sensor Circuit High Voltage
P0603 - Control Module Long Term Memory Reset
B1552 - Keep Alive Memory (KAM) Error

Last two may be from pulling battery power
Here's where you decifer the DTC's.
http://myweb.accessus.net/~090/dtcobd2b.html#bod

Which one of these should i be the most concerned about?

The first two. They are likely the same problem. I would assume you are having fuel guage problems? If not, clear 'em and see if they return. You didn't mention if they were current or history.

They were history.