what would cause a 2001 cavalier to bog down while driving and have a rough idle

One thing to look at would be catalytic converter. If this is getting plugged you will notice loss of power worse fuel mileage and the exhaust will sound different. With a rough idle one thing to look at is EGR valve. One good diagnostic tool that works is a vacuum gauge. Hook the gauge up to manifold vacuum. You should see 17-21 In. Hg. on the gauge at idle and the needle should be steady. If you have anything other than this repost with what you have on vacuum gauge and I can tell you where to look next. A vacuum test is the best general engine condition check there is and it is the least expensive.

It maybe just your tranny, they tend to idle high and be rough, thats how they are I would guess the tranny.