I have a 92 V-6 Vortec Jimmy that I just recently got out of the shop after replacing a catalytic convertor, map sensor, spark plugs and wires...

before repairs, i had severe loss of power and a ton of black smoke coming out of the exhaust when i gun the engine...

after repairs, it is still slow (although much better than before) to accelerate but when it shifts after 45 mph...i can feel the hesitation or "bucking" as i like to call it. a small amount of black smoke is still coming out of the exhaust when i accelerate quickly.

bottom line, i spent over $500 to fix these problems and nothing is working. I've also replaced the air filter and put fuel injector cleaner in the gas tank.

any ideas as to what may be causing the sputtering and hesitation? i am at my wit's end.

One more thing...I am starting to suspect a vacuum leak...any ideas on where I can start looking?

i've spent my entire paycheck getting my car fixed (and it's my only mode of transportation)...any simple things I can check would be greatly appreciated.

Pull your upper plenum and check for washing...Sounds like you're dumping fuel

at the risk of sounding stupid....what is a plenum??

at the risk of sounding stupid....what is a plenum??

Top of the intake... You injection system sits inside.

Although I did suggest to the mechanic to check the plenum, the problem does seem to be fixed. They cleaned the fuel injection system and did an air induction (or reduction?) and the car is running much smoother. There is no hesitation after 45 mph and the car accelerates beautifully. The car has over 171,000 miles, so I know I'm not getting the greatest of gas mileage. I'd like to improve that. What are some simple things I can change to help imrove fuel consumption? The following is a list of what already has been replaced:
Spark Plugs, wires, distributor cap, rotor, map sensor, O2 sensor, air filter, catalytic converter, and the mechanic added some kind of special chemical to keep my fuel injection clean.

Pull the plenum... Check for washing. At that miledge more than likely you have a leaking cpi or nut kit which will be hell on your miledge.

Do a full tune up
Possible cold air intake
Check your suspension parts
Run a can of seafoam through the system
Keep your tires inflated to proper pressure
Hold many miles on your 02 sensors? They should be changed out at 75k or so