I just bought a 2000 impala 3.8 series 2 with 174000 miles. The cars is clean been very well maintained one owner very good buddy owned it. He just spent about $1000 on a complete tune up job a few months back. plugs.wires,fuel filter.and pump,airfilter and a bunch of new sensors. but the car has no power at all it idles really nice and smooth and revs right up in park but when you drive it it acts like its missing a little and the more gas you give it the worse it is you put it down to the floor and it falls flat on its face and has no power at all You can drive it fine as long as you dont need to accelerate too much. Any ideas I thought maybe catalytic converter of maybe mass air flow sensor.?