I have nearly the same issue, all mounts are new, exhaust new w/hangers not touching even in drive w/ brakes on. Alt mounts new. On mine it feels like a misfire or vac leak at idle. at 1700 it is the worst and on take off it makes the car feel like a piece of junk. The performance is down and so is the mileage. My tranny has unknown mileage but the engine has approx 170,000 with a overhauled head approx 16,000 mileas ago. I am thinking I have a headgasket leak between two cylinders or a bad transmission pump or other bearing in the trans. There is a loud vibration and the car sounds like it has a very loud fan under the hood. ( clutch and fan blades also new).
I am going to do a leak down test and a compression test over the weekend and I'll report back. I have spent a lot of money and time on this car and this problem which is getting worse makes me want to buy something else. My last resort is to swap the auto tranny to a different one, I have one with 131,00o miles on it and I drove th car it came from it was good before I pulled it. I am just sick of working on broken things.

car is a 1991 780 w/ B230ft and aw-71 trans