Driveline vibration

'88 Toyota Sunrader RV 21'
22R-E A43D trans 110,000 miles
At speeds over 55 mph there is a heavy vibration in driveline. Doesn't happen at all speeds, but rather depending on how much gas I give it. Mostly when climbing slight grades, disappears with gas pedal to the floor - reapperas with a little less gas - goes away completely if I remove my foot from gas. Like there's a specific range of torque that gets it shaking. I've replaced carrier bearing, drive line cv's and rebalanced drive shaft. Can't tell which end its coming from, but traveling on highway causes marital unhappiness. Afraid to drive it on upcoming vacation. (I made a small donation)