Great! The trouble with internet troubleshooting is getting off on tangents. We all have had issues of our own at some time and pass them along...the trick is not all issues are what we had.
The guys who have been around a lot of issues know better...and that doesn't just mean guys that have been boating for 70 years or have owned 15 boats. You need the experiences of guys who have worked on hundreds if not thousands of boats. They will try to put your brakes on and make you focus on symptoms rather than jump to conclusions.
Wise mechanics know that it's usually something simple...look there first...as many pointed out that 2 trannys with the same symptoms rarely go bad at the same time but the voltage (and/or total electrical system) feeding those electric gauges is common so starting there has some promise.