Laboring engine

[Silver Blue '97]

First, I want to thank all of you in advance for all the help you have provided me in the past.

Here's my problem, when I'm driving around town the engine seems and sounds fine. However when I have to pass someone or have to accelerate quickly the engine sounds like its laboring. No SES light, just installed new AC Delco plugs and wires, any help would be greatly appreciated, and thanks again.