1996 Blazer Acceleration Problems/ Fuel Mileage

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I have a 1996 Blazer with roughly 103,000 miles on it. 4.3L CPI engine. I am averaging about 200 miles per tank, or about 11 mpg. Smells like gas outside the vehicle. Starts right up without a problem. Go to accelerate up to about 20-25 mph when cold and the engine just about dies, like it is flooding. Sometimes backfires through the exhaust too. Feels like an old GM car with a quadrajet 4bbl carb (quadra-bog) if you dump the throttle from a stoplight. Had the injectors cleaned about 2 years ago and the intake manifold gasket replaced at the same time (normal 4.3L problem). Had a trouble code for an O2 sensor low voltage a few months ago but cannot remember what code number it was and have not had a SES light come on in about a month.

Tired of running through so much gas. What steps should I do to try and locate the problem and fix it? Thanks, Gregg

1996 Chevy Blazer 4.3L CPI
2001 Chevy Venture 3.3L