Heavy misfiring on sudden or heavy throttle

Hello, I have the car listed above it is the LX model with the 3.0 V6 Vulcan engine. I have a really annoying problem: My car hesitates and shakes like crazy when applying sudden, medium or full throttle. I have replace: Plugs, wires, fuel pump, fuel filter, ignition coil, air filter, cleaned EGR valve, throttle body, IAC. Checked TPS, MAP. Checked distribuitor, vaccum Lines and so on. The interesting thing is, It does not hesitate or lose power on reverse and on neutral, it only hesitates or loses power while going forward. I also changed my transmission oil but the hesitation did not go away. The problem seems like is coming from a power cut because my rpm's goes crazy while hesitating, I can barely drive on a steep climb because the car seems to loose electric power or fuel delivery causing the hesitation. Please help. Thank you