Just ordered a thin spark plug wrench for BMW motorcycles because mine didn't fit, only to find that there is one included in the toolbox under the seat
I'm absolutely no expert on chasing these vibrations, but i think it can still be your torque convertor. A damaged friction material ring can cause an unbalance in the TC even when not in lock up. In lockup however it will be worse
About your first note, the hard 1-2 shift. I had the same issue with my stock '91 K5 with 700r4. I adjusted the tv-cable multiple times as described but that changed nothing. Until somebody gave me the advice to adjust it one notch further manually and after that it felled like a new...
I had the same problem. Adjusting the doors so that they close firmly did a lot. Now i have to slam them a little harder but it really helped.
Then i added this, which also helped a little.
I does with
I does fit with a little modification. I idd this on my 91 k5 long time abo.
https://www.gmsquarebody.com/threads/factory-gm-guages-add-tach.23640/#post-451290
Be carefull, my ignition switch caught on fire a couple of weeks ago. I was only able to stop the fire by pulling one of the battery cables. Just shutting down the engine and pulling the key was not enough. Apperently the switch was so worn that the metal glider got in contact with a constant +.