Shudders when driving. on 2000 Honda Civic

My Civic shudders intermittantly when driving on a smooth level road. It does not do it when shifting( it ts an automatic) or under power. When I let off the gas it stop shuddering. My local mechanic says it could be transmission. I tuned it up( plug, wires, distributor cap, etc. but that didn't help anything but gas mileage. What could this be?

2 answers 1 comment
I would check your INNER CV joints. They often make rumbling/vibration when under power. Good Luck!
Mine does the same exact thing. I have an automatic, whenever I drive and let off the gas it will shake at a certain point. I still have to get it fixed, but I was planning on getting it switched from auto->manual when I get back from my deployment here. I was wondering will that clear the problem up? I am not getting it switched for that one reason but I would like it to be manual.
check front axles