Plugged up EGR system can bog engine mightily. If you haven't cleaned it in some time it probably needs it. Include the passage behind the throttle body that's cast into the throttle chamber. You'll need to pull that big cap at the firewall end of the casting to let whatever you blow out/drain out. While you're at it you might want to give all the vacuum line fittings that sprout from the throttle chamber a squirt of carb cleaner.
On some of mine the insides of the vacuum lines were filled with a tarry goo that filled the ports (good time to change out the vac lines if they are filled with goo). Check the back pressure transducer too (brow top shaped thingy). It supposed to let vacuum pull open the EGR valve when the back pressure from the exhaust system pushes an internal membrane which opens the vacuum passage. If that membrane ruptures it lets hot exhaust gas into the transducer and that's the end of that device. Bubbly looking top is a good indicator it's cooked. Isuzu has to match the numbers to replace it so bring it with you when you go to the counter.