2001 HONDA Accord rear end vibration

So I’ve been experiencing some shaking in my automatic 2001 Honda Accord EX Coupe 3.0L V6. The shaking starts at about 40mph and can last up to about 55-60 mph when it starts to fade away or become unnoticeable. The shaking is a lot more noticeable when your on an incline and accelerating. The shaking feels as though it rocks side-to-side but my steering wheel doesn’t shake or pull. I’ve gotten my car tires/wheels balanced, replaced the wheels/rims, go new tires, had everything balanced again, and got an alignment done. Since I used to think that the shaking was more prevalent in the back end of the car, I replaced the sway bar link stabilizers as directed by a friend. Needless to say, none of those things stopped the shaking. My first set of wheels/rims had one bent rim, so it shook because of that and couldn’t really distinguish that there was something else beyond the bent wheel that could cause the shaking. So that’s why I had to replace those wheels and tires. My new wheels required hub rings so discount tire put those on when installing them.
I’ve had my car lowered using lowering springs, which dropped the car about 1.8-2 inches. I had that done over a year ago and really don’t think that’s what would have caused the shaking. I say that because I’ve had those springs for a pretty long time and I wasn’t experiencing any shaking after installing them. I know that my car doesn’t have a stock camber kit that allows for lowering the car. But I’m not worried about the camber even though it does wear out the inside of the tire faster than the outside. I’ve had my exhaust done as well. It goes from the catalytic converter to the back (cat-back) with a 2.5 inch piping. There’s no leaks or anything and it’s not loose either. And those are pretty much the only things I’ve done to upgrade my car. Of course I get regular oil changes and I recently did a transmission flush (drain and fill). I’ve been reading up on what could cause the shaking, through online threads, and all I can see that might be the cause is the CV axles? They’ve had the same issues that I’m having, replaced the axles, and that fixed their shaking. I pretty much covered everything I could think of. Thank you for your time and help.

Why do you think it’s a rear end vibration? The fact that it’s most evident when the engine is under load suggests the vibration is in the drivetrain, all of which is up front.

Most likely I would suspect the CV joint(s)/axle(s) as you mentioned.

Shaking that starts in the 40s or so and lasts through the 50s or so and return on acceleration to me always brings a faulty torque converter clutch. Would you describe it as ever feeling like driving over a washboard? How many miles are on it? Has the transmission ever been serviced? (Or replaced? Honda had terrible transmission problems around the '01 years)

The other thing it brings to mind is a CV joint problem as note by jesmed. That would go a lot more with acceleration rather than speed - but it also might only show up on acceleration above certain speeds.