I think I would do a bit more diagnostics before diving into replacing the axles. A bent axle will usually create a vibration whether the engine is under load or not or speed. Wheel balance, worn engine/transmission mounts or worn suspension components are a few things that could cause the problem you describe.

 

X2 Unless you like to keep buying and putting on parts until it is fixed. When I have a problem that I cannot repair or understand I take my car to a trusted mechanic. This way your not playing the "maybe" game. What could it hurt. Might cost $50 for a diagnosis, but better than dropping 2 bills in axles and all the time, only to find out that never solved the problem. And now your buying more parts that may or not solve your issue.

 

I am speculating here, but since you are fairly certain it's not the cat. Could it be the transmission? Mine does something like that periodically and when I shut the car off it goes away, seems to happen on hotter days but could be coincidence, anyways it could be one of the solenoids sticking in the tranny as these cars have a tendency to have tranny problems related to the solenoids

 

not sure about the transmission. im doubting yet also wishful that its not tranny related. if so, ill ride it out until it's final tow before i have the tranny replaced again. i bought a pair of axles from oreilly's ...... get this ..... in Dallas , mostly every mechanic shop REFUSES to install parts that they didnt sell you. instead they would rather get it from oreilly's themselves and triple the part's price in addition to the high labor charges. found out that 6 shops who turned me down all get their axles from oreilly's too. source = the oreilly's sales attendant who sold me the parts.

 

You could get a new down pipe with a high flow cat from zzp. If you willing to spend the money. I think its worth it.

 

guys, thanks for stickin with me in this thread ....... the axles turned out to have been the problem. replaced both of those bad boys for $200 bucks....... now my baby is ridin like a champ again. if your car shakes during acceleration, but coast just fine when your foot lets off the gas ...... you probably have the same issue as me ...... have your axles looked at! thanks guys