A few problems with my 97 blazer . . .

Hello all, this is my first post in these forums I hope someone can help me

Back in December 2003 I bought a 97 Blazer 4D 4WD LS with a V6 Vortex

Since then the only things I have replaced were the entire AC system and the fuel pump

1 - I have been hearing a really loud Vacuum type noise from my engine when I accelerate for the past few months and I don't remember if it did it when I first got the truck (it usually goes away once I hit 50mph), it does not make this noise EVERY time I accelerate, I would say about 30% of the time and my engine temp has never risen above the half way mark

I was told by a mechanic (who owns a GMC jimmy with the same engine) that this is a normal noise for that type of engine

I want to know if this is in fact a normal noise and if not what might be causing it?

2 - I had have 3 instances where I am driving and my oil pressure gauge drops to 0 and my "check engine" light comes on, this usually lasts for about 5-10 seconds then goes back to normal, I think this might be a clogged oil pump but I’m not sure, any ideas?

3 - Some times when I get in my truck and put it in reverse and then let off the brake I feel a small bit of jerking when it starts moving back, any ideas?

Any help would be apreciated

I am also a bit confused on which gear i should use for regular in town driving

I was told by the owner to drive it in 3rd gear around town and use overdrive only fo freeway driving and when i am pulling loads

you could even try cleaning the throttle body you would be amazed at how dirty it gets. Some times the throttle body can make vacuum noises.