Help with Diagnosis - '02 VW Beetle Automatic

This one's a bit weird and I need some help. Here goes:

2002 VW Beetle automatic with ~130k on the odo. Belongs to my daughter who lives in Missouri - I'm in Michigan so I can't drive it myself. She's not a car person.

Below 40mph, the car drives normally. Above 60 it drives normally. Around 40 it starts to shake, building to a strong shake she feels in the entire car, which then eases off as she gets to around 60. She says she doesn't feel it in the steering wheel. When she lets off the gas, it stops. It only occurs when accelerating or under a load (uphill). No CELs or other warning lights are present.

When she first described it. I thought maybe she lost a wheel weight, but that doesn't track with the behavior she describes. What else is speed and load dependent that isn't felt in the steering? Half shaft? Cv joint? Torque convertor? She's gonna check the obvious stuff - tire pressure, lug tightness, trans fluid level, but I think that'll be unrevealing.

I'm stumped - what do you think?

Anyone.

Beuller?

Could it be an engine miss, or is the vibration frequency tied to speed?

Worn out dog bone?

I have had wheel balance do something like that. Could be engine mounts or CV joints.

She's gonna take it to her mechanic, but as a new teacher trying to pay off student loans, money is tight. Dad's gonna have to help on this one...

Its overdue for a front suspension rebuild at that mileage too. Make sure any parts that get replaced are OEM VW, there is some pretty terrible aftermarket junk for those cars that wont last long at all.

Not feeling it in the steering wheel... Could it be an issue with BACK wheel(s)?

My Protege did something similar with a poorly rebuilt axle, but the vibration never completely went away. It was just more noticeable at certain speeds.