Down shift it into 4th or 3rd and floor it. It should accelerate decently, if it doesn't you might have a stopped up catalytic converter. If you do it at night, hold it floored for a while, then quickly slow down pull off the road open the hood and see if the exhuast manifold is glowing. If it won't accelerate any harder, and the manifold is glowing, your cat is plugged up probably.