According to the FAQ on Dennys Driveshaft website:
How much slip travel should I have?
In most applications the minimum is 3/4 inch and more than 1 inch is not necessary. This is measured with the rear suspension supported on safety stands or with the rear end on the ground.
https://www.dennysdriveshaft.com/frequently_asked_questions.html#faq_id10
You may have other issues as well, but you clearly have way too much travel on the slip yoke. You push it all the way into the transmission and then pull it out 1 inch. That is where the yoke should be when the driveshaft is bolted to the differential and the car sitting on the ground on the tires.. Fix that first and then try it, before making any other changes.
