Odd vibration

Hello everyone.

I have a 95 Wrangler. Stock axles with 4.10 gears, Detrioit locker in
the rear, lifted, and just recently, a sye and custom drive shaft. I
did the sye because driveline vibs killed my t case. So I had to get a
new case, and did the sye. So I installed this drive shaft and case,
and removed the tcase lowering kit, and my bad vibes went away. But
only a month later a new vibe has appeared. I really don't notice it
until I'm around 40 mph or more and let off the gas. This is a five
speed. And while coasting, it has a vibration. I don't feel this
vibration thru the steering wheel or shifter as I did with the last,
so I'm thinking not a driveline vibe. Any guesses? I'm puzzled at this
point.