Oldsmobile/Buick Repair: still stalling after tune up, fuel injector cleaner, muffler shops

Question
98 oldsmovil bravada 6 cyl 4.3 4x4
tune up was performed in this vehicle and a fuel injector cleaner was added to the gas tank and the gas tank was filled. car stalles very bad, i have to give gas little by little untill engine comes to a normal idleing to run good (takes like 3 minutes for the car to run to a normal pace). i put new wires, spark plugs, gas filter, air filter...check the gas preasure it gives me 56 (the book says it should be over 41, what do you think i am missing?
please help!

Answer
Hi
Fuel pressure SHOULD be 60-66 psi.
I would recheck fuel pressure.
I would also having the Catalytic converter checked.
Most muffler shops will check cats for free, or for a reduced rate.

That would be my first 2 checks.
Hope this helps
Pawl