What are the differences between the 4T60e and the HD version? I only ask because I am having a terrible time getting the correct right axle. The listing at Advance and NAPA both show a different axle for vin 1 than the n/a application, but it'* about 3/4" too long, the listed number for the n/a application fit. My tranny mechanic wants to replace them again for troubleshooting (not a big deal, I have a parts "in" and we are chasing a high speed vibration) so I ordered the listed axles thinking the right side will be too long again. If the physical dimensions of the two trannys are identical, my fears are calmed (meaning only internal changes), if they are different, I might be looking at the fact that someone may have shoved a nonHD tranny in my car during a prior owner, if this is even possible ........ ULP! Of course, it could just be an application listing issue with Advance and NAPA'* supplier which is the same.

BTW the part numbers from both are listed as:
Left 9483 fit
Right 9570 too long
Right that fit 9484 (n/a listing)

And before you ask, they were replaced because I rebuilt the suspension, easy access, showing a little wear on one boot, and the price was right, and my bonnie is my hobby.

I can't help you with the axles but the high speed vibration might be something you have not thought about. Have you lowered the car at all or has it sagged over time? If the car sits lower the axles are no longer running "neutral". In other words no angle. Another thing that can cause the vibration is the engine mounts collapsing. Again with a lower engine the axles are no longer runniing "neutral". This is one place to look. Hope this helps.