Well, Pelle, if you are reaching 5000 rpm, then it's unlikey that it's fuel delivery. You are near the top of the safe rpm range for the M103 motor. You didn't mention whether or not the engine seemed to be breaking up, ie. go stop go stop or perhaps a high speed surge. The sound you are hearing could be a high pressure exhaust leak, associated with high engine speed, which might just point to an obstructed cat. Has the car burned a lot of oil,has it had valve guides,seals done. What is the mileage on the engine? Another thought is the distributor cap and rotor. Have those pieces been replaced or checked?
2000 Dodge Grand Caravan SE
No matter what you fix, there will always be something else to fix..
"Warranty" is just another way of postponing the inevitable.