First and foremost, make sure you can remove the fill plug before draining it. Since you need to remove the shifter to pull the trans, you'll find it much easier to refill it through the shift tower while you watch for it to overflow out the fill hole. Also use the right fluid. Not GL rated...
I recommend loosening the top e-torx head bolts first. You can't get at them with long extensions before you drop the cross member and tip the back end down. I remember the bellhousing on my AX15 wouldn't clear the frame rail while on the jack. I had 6" lift on 32s and thought I'd have...
There are small tabs on either side of the terminal that need to get pressed inward to slide them out the back. One of these https://www.amazon.com/Depinning-Electrical-Connector-Extractor-Automotive/dp/B0922GF9W8/137-6170536-0341610 might do the trick.
When I refurbished my panel, I just...
A common place for wiring issues is where the harness crosses from the injectors over the firewall. See if wiggling it makes skip while idling. Wiggle the injector clips as well.
That sounds like the ignition switch needs adjusted or replaced. The switch is under the dash on the bottom of the column, actuated by a rod the runs under the column. You can loosen the two screws and move it for or aft to adjust, but it's also common for them to burn up and need replaced...
Given the dependence on rpm and not speed, I'm going to say it's one of the bearings or planetary gears in the trans. 1991-1997 AW4s are interchangeable. You'll have to cut and splice one connector unless it's a 1997.
Coolant flows through the bottle, coming in from the top and draining out the bottom. When running, it might look like its boiling or bubbling but it's not.
The cap on the pressure tank is a known failure point. The replacement tanks flex and the poorly made caps tends to not hold pressure or work loose, causing a loss of pressure and a boilover. I had one that would open a 6-psi. A cap for a 710 Volvo has much better formed threads and holds...
Is it perhaps the torque converter locking and unlocking? Does it stop if you lift the brake pedal up or lightly press with your foot? That would point to the white switch high up on the brake pedal being misadjusted or dirty. As cruising speed, lightly tapping the brake pedal should trigger...
No real advantage to doing it while swapping the trans, aside from motivation to get er done all at once. Trans doesn't need to come out to do the rear main seal. Of course, confirm the seal is bad and the leak isn't from higher up first since all the major leaks tend to flow back and drip off...
The fuel pump will run briefly when the key is turned on, then stops until the engine computer sees cranking. No codes? It could be the distributor sensor too.