1995 blazer 4.3 v6 vortec cpi hesitation problem
 

my blazer hesitates when going up a mountain or passing a car sometimes usually notice more on sharp steep mountain curves and you can hold the motor wide open and it fall on its face and the rpm slowly rise then all of a suddenly it wakes up at about 2500 rpm don't know what is causing it seems like a timing advance issue to me no check engine lights just replaced o2 sensors because thought that was it but it wasn't has new spark plugs wires and cap and rotor. seeing if anyone else had this issue with there 95 blazer sometimes it doesn't hesitate tho which is weird. thought about replacing crankshaft sensor and camshaft sensor to see if that helps.

Check the fuel pressure first, before you buy any more parts

if the pressure was low wouldn't it not run at all? because I thought these cpi motors at to have 52-60 psi to even run

On paper the spec is like 56-60 or something. But, in my experience (and I've had some experiences with the fuel system on these trucks!) they will idle, and run at low load on less psi. There is no spec for fuel psi while the engine is running. But when my pumps were going bad, the truck would idle, and drive at very low throttle inputs. Once you gave it more than quarter throttle, or had to take off up a steep hill, it would fall on its face, misfire, sometimes stall out completely

It only falls on its face from 1800 rpm to 2500 rpm when a high load is put on the engine after that it wakes up and gets its power back the only way to tell if it is a fuel pressure problem would be to get a scanner and a digital adapter for the fuel rail to drive the blazer and look at the pressure while going up a steep hill that is why I thought it might be a timing advance problem because it doesn't misfire when it falls on its face it just has low power then wakes up I do know the fuel pump is pretty loud on my blazer tho the longer you run it the louder it gets it is very loud after driving for a few hours. I might replace the fuel filter and see if that helps but I doubt it

I'd rather use schrader port and follow the sticky thread.

Check your pressure at the test port, and test it at the fuel pump (either directly on the fuel pump output, or at the fuel filter fitting) and let us know the results.

Anything else will be throwing time and money at it, and hoping something sticks.

It might very well be timing or whatever you think it is, but your symptoms sound very similar to fuel pump issues I have had in the past.

will do the pressure tests after replacing the filter and see if it still acts like it does after filter replacement thanks