throwing random misfire,cat,long shift,incorrect gear ratio, and fuel level on 2003 Buick Park Avenue

sensor codes also air ride has the rear suspension all the way up.have replace the cat, the O2 sensors, plugs, wires coil packs, ignition mod, EGR valve, intake gaskets, fuel filter, serviced tranny... at a loss.. when the engine is running smooth,the car shifts smoothly, when it runs rough, it doesn't want to shift and when it does it slams into gear.. could the main computer be the problem and if so is there a way to test it?

Asked by for the 2003 Buick Park Avenue
sounds like you need to quit throwing parts at it and get a diag from a good tech to get the car don't mean repl parts,its telling you there is a circuit issue. good luck
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