codes

99 Suburban with a 5.7, had a code PO430. Investigation indicated O2 sensors. I changed the sensors this week, codes were clear for 150 miles then I got the dreaded check engine light back. Now, in addition ot hte PO430 I have PO339, which indicates crank position sensor. I put new bushing and ear in the distributor a year ago to get rid of a PO339. Amy thoughts on what might be going on? Truck burns a quart of oil in about 1700 miles, has 180,000 miles on it. Intake manifolds have been done. Timing chain was done at 150,000.
I am thinking the cat is bad for the PO430, despite the definite O2 sensor reading from the garage's scanner. Not sure what to think for the PO339.
thanks very much for any thoughts that you might have - I appreciate it.
Bill