I have a 3.9L in my collection with about 120,000 miles on the clock. I seem to be getting decent response in the lower and upper RPM ranges but the mid-range is very sluggish. Does anyone have any similar experiences and/or solutions?

Thank you...

 

What sort of tune related work has been done on your engine in the last years, have you replaced the spark plug wires, how about the O2 sensors.
What gas octane are you running, have you ever de-carboned the engine?
Mike