1995 Oldsmobile Aurora Hesitates at 45 mph

I just bought a 1995 Oldsmobile Aurora with 132,000 miles. When you start moving its fine but at 45 mph the rpm's drop from 2500 to 1500 and the engine hesitates and sputters and there's a clunking sound coming somewhere in the under the hood but if you give it gas the rpm's go up and it does fine with some sputtering. Also if you floor it, it hesitates through all gears. I can feel the Idle air control pushing against the gas pedal when i let off the gas. The I.A.C also clicks about 7 times when you turn the car to on but don't start it and when you shut the engine off. I've checked everything the injectors, fuel/air filter, hoses, catalytic converter, and even sprayed the throttle body with cleaner and cleaned the butterfly valve . WHAT'S WRONG WITH MY CAR!!!!!