I just purchased an 02 Duramax and im wondering if its normal for the oil pressure to be 3/4 to almost max while driving.... around idle its 1/4 or lil below 1/2 on the gauge. These conditions normal?

thanks

Yes, Depending on what type of oil(synthetic) you are using it may go down a little. Some have reported as high as 100 psi with an additonal gauge.