truck shakes or vibrates when i decelerate from 60 mph, but stops shaking immediately if i accelerate

What is your question?

The truck starts immediately and runs smoothly. When it gets to 60 mph, it continues to run smoothly, as long as they is slight acceleration. If I stop accelerating and coast, when the speed drops to 60 mph, the shaking will begin. But the shaking stops immediately if I accelerate. My truck is a Nissan Frontier SE pickup, with 136,000 miles

What makes this problem better or worse?

When I accelerate when the truck starts shaking, it stops shaking

How long has your 2005 Nissan Frontier had this problem?

three days