1995 Chevy Blazer LS Vortec VS Rough Starting

Hi Everyone, I have read many posts close to my problem, but not quite exact. I have a '95 Chvey Blazer V6 LS CMFI Vortec with 96,000 miles. Had the gas tank replaced about a year ago along with the fuel filter and the truck ran perfectly.

Now about the last 2 months when the truck sits and we go to start it in the morning we turn the key to on you can hear the sound of the fuel buzz for 2-3 seconds then turn the key and she fires up like nothing is wrong after sitting all night. Gas mileage has dropped too. Just Great.

Here is the difficult part: It will start perfect sometimes. Other times it will crank fine and not fire right up until you push the gas and then starts. Other times you will push and pump the gas pedal and slowly let up and then it will fire right up.

Drive it. Let is sit for and hour - fires up other times it won't.

I thought maybe the injectors were clogged. I have added Berrymans Chemtool B12 & Marvel Oil about 3x back to back to the gas when filling up and this had dramatically improved the startup, but intermittently, not always, still needed to press the gas pedal when attempting to start at times. It did not fix the hard starting, but did improve it.

I am not a mechanic - I can do brakes, I did change the the EGR, alternator, starter and things like that on vehicles, just to give you a basic idea of my mechanical background. Reason for this is some of you are great mechanics out there and I might not be as mechanically inclined to do what some of you may suggest. Would love to though with the economy and the costs involved to fix automotive issues. So hope you folks can shed some insight, please.
Thank you

Check fuel pressure and leakdown rate. Ignition ON, (do not start the engine) fuel pump running during the 2-3 second "pump prime", fuel pressure must be 55psi to 61psi and must remain above 50psi for 10 minutes after the pump shuts off. Post your results.