In your posts, I haven't seen any mention of tune-up history (ie plugs, wires) and also, what brand oxygen sensor did you install? GM cars run like dog-doo on Bosch.
For clarification, the correct fuel pressure spec I show matches what bearwulf listed, 41-47psi key on/engine off, and a 3-7psi drop (38-40 minimum, with 40-44 psi preferred), car running with FPR vacuum attached. Your fuel pressure seems a little low, but could be considered within spec allowing for a 5-10% margin of error on your guage.