hesitation/delay in power

I have an '88 blazer with a '92 2.8 V6 Since changing the motor i have noticed that while I'm up to speed whatever it may be, that when i let off the gas and romp on it I have a delay or slight hesitation before it takes off. For instance if im cruising at 55 im running at 3000 rpm when i let off the gas it will drop to 2000 rpm then horse it and it will hesitate around 2500 rpm as if its pulling a load for a second. Any help would be greatly appreciated

check pluged exguast like catconvertor