Ihave a 94 s10 blazer, with the 4.3L V6 vin W.I was wondering, if the brand, and weight of oil really matters. It has 136,000 miles on it.I have been putting in Valvaline high milage synthetic blend 10-40w.My oil pressure gaugemoves more then my tach. Up and down,I thought a moreheavy oil would help. Next changeI am going with Valvaline 20-50w or higher.
Any suggestions?

 

There are some people who are very **** about what oil to use...

So I will just tell you what I use...

pennzoil 5w-30

I have 412,000 miles on my truck about half of those on this engine, truck runs fine doesnt burn or leak any oil all is well

 

Cody, the 4.3L is not picky about its oil. Just about any name brand is going to do good in it. Running a 'high milage' oil is fine for the miles on your truck. The only thing I might reconsider is the viscosity you're using. Unless you are having consumption issues or using the truck under pretty hard conditions regularly, that's a little thick on the top end viscosity. In a HM type oil ( which usually is at the upper end of its rated viscosity range, anyway) I would think a 10W30 would be good for you in Utah. Some would even say a HM in 5W30 would be okay.
About the oil pressure gauge, what type of fluctuations are you talking about? It's normal to see the pressure change between idling, cruising, or accelerating. On average, idle pressure will be from 40-50 psi, cruising from 50-60 psi, and accelerating from 50-70 psi. As long as you get 10 psi for every 1,000 rpm, you're safe (that's an old rule of thumb).
As for what I use in my '02 Blazer - Havoline 10W30 conventional oil.

 

wellI was starting to think the 20-50w was kinda heavy.
My oil pressor gets as low as 30psi, and up to 70psi.

 

If that represents the difference between idling and accelerating, you're fine.