Your tranny problem is the stuck pin -- if it won't move, it cannot transmit pressure to the control valve the modulator operates. Clean it off, clean the bore (no abrasives, please) and see it you can get it to slide freely. If not, get a new one. Also make sure it isn't in backwards -- I've not seen one, so I don't know if you can install incorrectly or not.
Does the tranny shift more firmly at wide throttle? If so, the modulator is working.
Another thought is to replace the filter in the tranny, but a filter and fluid change on an old transmission can be worse than leaving it alone.....
That braket is a possible source of the vibration, by the way -- it is supposed to have a clamp on it that holds the exhaust up at the rear of the tranny. No bracket, and it will vibrate badly at resonance speed, and cause the exhaust to drum on the floor pads. Also check the rubber rings that hold the exhaust up at the rear, if they are stretched or broken, the rear muffler will pound on the body pad there making a horrible thunder.
The rear tranny mount gets soft when it goes bad, so the tranny can move up and down. This causes a drumming on acceleration, otherwise it's usually quiet.
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!