[leebrown66]

It certainly shouldn't shake the way you describe. If it's speed and not rpm's and no unusual noises, things I could image having that effect, and apologies for asking the obvious:

Are both wheels true?
Are both wheels balanced?
Are both tyres in good shape (as in round)?
Are both tyres inflated to correct pressure?
Is the steering pre-load correct?
Is the chain correctly tensioned?
Are all the engine mounting bolts tight?

 

[leebrown66]

Some motorcycles consider it rude to discuss their age, let alone their sagging parts 🤣