since you have changed CPS CKS im thinking you have access to a scan tool and this has been area of difficulty. If so
Collapsed air intake duct
Restricted air filter element--Refer to Air Cleaner Element Replacement
Fouled spark plugs--Refer to Spark Plug Inspection
. If the spark plugs are fouled, determine what caused the condition.
Engine mechanical condition (worn timing chain and gears, low compression, etc.)--Refer to Symptoms - Engine Mechanical
in Engine Mechanical 3.8L.
Restricted exhaust system--Refer to Restricted Exhaust
in Engine Exhaust.
Faulty engine coolant temperature (ECT) sensor or Air Intake Tempurature Sensor
-approx. range 3520 ohms at 68 F to 9420 ohms at 32 F
Faulty manifold absolute pressure (MAP) sensor--Refer to Manifold Absolute Pressure (MAP) Sensor Diagnosis
Stuck throttle position (TP) sensor--Refer to DTC P0121
can you read engine rpm with scantool?
are there any DTC codes stored?