I just purchased a 2003 Tahoe z71 with 100k on the clock. I went and got my oil changed earlier today (think they used 5w-30). Took the Tahoe out tonight and it was acting super strange at idle. Oil pressure would sit at 40 then slightly drop to 38ish causing the rpm's to drop and dash lights to dim. Basically almost stalling. I have been searching like crazy tonight and can't seem to find a cause. Some people are even saying this is normal with the vortec. Any insight would be appreciated because I'm starting to stress its something major.