Vibration on the floor underneath gas pedal

were the motor & trans mounts checked?

check the "u" joints for looseness and wear especially the front drive shaft . check sliding splines . The vibration is a harmonic vibration normally associated with worn "U" joints --bent or out of balanced ---worn /seizing slip joints or being excited by a failing drive thrust bearing in the diff. ( big bearing directly behind the pinion gear that takes all the load on drive) check the magnet on the diff drain plug for metal bits.

Accelerator Pedal Position Sensor needs replaced

Check your spark plugs.

ENGINE HESITATES WHILE ACCELERATION

LOSS OF ACCELERATION

It can be fuel pressure issue or it's the problem with accelerator pedal or its clogged filters causing there.

There are many other possibilities. I suggest you to go through the list of help links mentioned below, these will help you to confirm where the actual fault lies: -------

Jerks and Hesitates During Acceleration?

http://technoanswers.blogspot.in/2012/07/2004-dodge-town-country-jerks-and.html

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Loss of acceleration?

http://technoanswers.blogspot.in/2012/02/loss-of-acceleration.html

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Headlights flickering and car hesitates to start?

http://howtobyme.blogspot.in/2012/02/headlights-flickering-and-car-hesitates.html

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How exactly the Vehicles Accelerator Cable works?

http://repairhelpcenter.blogspot.com/2011/11/how-exactly-vehicles-accelerator-cable.html

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How exactly Vehicles Accelerator Pump Diaphragm Works?

http://repairhelpcenter.blogspot.com/2011/11/how-exactly-vehicles-accelerator-pump.html

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2000 Toyota Avalon: Engine Lean Codes and Knock Sound on Acceleration?

http://whatisbyme.blogspot.in/2012/05/2000-toyota-avalon-engine-lean-codes.html

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2004 Toyota Avensis: Acceleration And Deceleration makes noise on Front End?

http://whatisbyme.blogspot.in/2012/05/2004-toyota-avensis-acceleration-and.html

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Wheel hop under hard acceleration?

http://technoanswers.blogspot.in/2012/04/wheel-hop-under-hard-acceleration.html

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2009 Chevy impala accelerator pedal sensor?

http://technoanswers.blogspot.in/2012/02/2009-chevy-impala-accelerator-pedal.html

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Nissan Pathfinder stalls and bucks on Acceleration?

http://technoanswers.blogspot.in/2012/02/nissan-pathfinder-stalls-and-bucks-on.html

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Acceleration lag problem?

http://repairhelpcenter.blogspot.com/2012/01/acceleration-lag-problem.html

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These details will help.

Thanks.

bad tire, gad wheel bearings , loose steering tie rod ball joints , wheel alignment
take it to a front end specialist for a full inspection

How about motor mounts.

I think it would be a good idea to check your fuel filter....The most likely place for it to be mounted is in the engine compartment, or if not there it'll be underneath, close to the tank.....Regards Johngee

It may be the transmission input shaft bushing or bearing, located in the rear of the engine crankshaft, in front of the clutch assembly. If the bushing or bearing is dry (needs to be greased), the input shaft will still try to turn with the engine rpm, even though the clutch pedal is depressed. Also, the clutch disc may not be fully releasing, which could possibly be corrected by adjusting the clutch pedal linkage. good luck

check the drive shaft between the intermediate transmission and the front transmission for miss alignement and defectivness of the telescopics system of this shaft. we had about the same problem on our 1996 same model...