Need Info on 1999 Blazer 4X4

Hello all, I need some help with my 1999 Blazer. I did an oil change about a week ago. After the oil change I noticed that the oil pressure is sitting between 1/2 and 3/4 (275 kPa - 300 kPa), I think this is too high but I don't really remember what it was at before. I changed the oil. One GM dealer says it's WAY TOO HIGH and I should bing it in right away for service and another one says It is fine. After a bout 20 mins of driving the pressure seems to drop. The pressure goes higher when I am driving and gets lower when I am sitting at a stop sgn or red light.... So I guess my question is that if you have a vehicle with the Vortec 4.3L V6, the next time you start up your truck can you check what the oil pressure it so that I can see if I am in normal range.