90 Z24 hesitation

I have a 1990 Z24 3.1 5 speed Cavalier. The car idles and runs fine until it's under a load, such as jumping on the gas or maybe a steep hill. I have replaced the plugs ,plug wires, control module, and coils. After doing this the car ran like new for about 2 months but now has the miss back. It's not a real bad miss just real annoying when you need to get on the expressway. Do you think one of the coils may be defective? I have checked them at idle and they all have good spark but maybe under a load it misfires? Right now I'm totally confused and don't want buy any more parts. If the damn coil pack in a better spot I'd change them out one at a time to see if it helps. Thanks for any help.