I have my 2000 Blazer on the road and so far compared to my 94 S10 with the older Vortec V6 I am getting an estimated 8-10 per gal.
What should I be looking for that could cause this?

My son had a 98 PU with the same engine and laughed that he had the same problem and I am also hearing this from a few others. He's laughing because he is now driving the S10.
Is there a "common" cause for this in the later generation Vortecs?

 

the 2000 is getting mileage like that? Yeah it's been happening to my 97 as well, as few things you could do is a full tune up, change spark plug, clean your filters, check your fluids etc, it probaobly will run better, but laugh at your son when your blazer outlasts his s10

 

When was the last time a full tune up was performed (plugs, wires, cap, & rotor)?
Are there any codes present?
Have you cleaned the throttle body, EGR valve, and MAF sensor?
Have you checked/replaced your air filter?
Tires properly inflated?
Tried switching fuel stations?
Have you tried running Chevron Techron Fuel System Treatment Plus through a few tanks of fuel?
How about a seafoam treatment (search for this - but do it before you change the plugs)?

 

Thanks swartlkk, that's the list of possibles I was looking for. I already had picked up the air filter today and planed on the full tune up, weather permitting up in Webster. I'm just stunned that I have no SES light and smooth running but such low MPH and never thought anything "routine" could bring it down so much.

The other thing I noticed is a feel of a drag even in neutral as though all or half the front end is always engaged, yet it is obvious when steering between 4wd and 2wd the absence of steering hop in auto trac or 2wd so if so it might be the front axle is loading on one wheel hub?

 

Maybe you have a brake dragging?

 

I thought that too but then I also notice at a stop light if I take my foot off the brake I start creeping forward on level ground with a normal idle which would not happen with a brake drag.
So doing say 40 MPH letting off the gas the vehicle drops in speed quite quickly, but at idle it seems to have no brake drag and actually creeps as though it is 100% free roling.
I notice in overdrive this doesn't happen until I coast a bit and the there then seems to be a downshift drag that I feel even if I shift to N.