Engine Performance problem
2006 Ford Taurus 6 cyl Front Wheel Drive Automatic 76000 miles
When I am on the highway & I need to excel past a slower vehicle, I'll press on the gas & begin to accelerate. But when I reach between 4000-5000 rpms, my car will dawg & shake for a bit, then return to normal (usually when I return under those rpms. Now, there is a day here & there to where it does not occur but those days are in the minority. This problem also occurs when I am at a standstill and then accelerate hard to above these rpms. Any ideas as to what should be repaired? Thanks so much for your help!