Re:
Anti-Surge - Anti-Hammer
Greetings Ron welcome to the Forum.
Wow, you've sure had a time with that Heater!
I'm not sure that I can give you an answer if the T/P is continuously leaking. That generally requires a replacement, which you have already done.
However,
If it leaks/drips occasionally, it sounds like you're having a surge problem, and it's just overcoming the relief pressure.
I'm thinking it's more like that, since you mention Showers and Dishwasher, since both of those activities, require valves to be opened and closed, specially on the Dishwasher part.
Do you have any Surge Piping installed somewhere (usually the Attic) ?
That would be a Vertical set of Pipes, just sticking up in the Attic, which are capped off, and usually from two to three feet high.
Idea for this, is to intentionally capture Air in the Pipe, where when a valve is suddenly closed, that the water pressure will surge up into the empty pipe, and diminish am instantaneous spike of pressure in your system. Sometimes they're called Anti-Hammer Pipes.
Look around and see if you have those, and if not, it's not all that hard to put a set in on the CW and HW lines.
The two empty Pipes is the Poor Mans way of doing this, they do make Gas Filled Cylinders that do the same thing, but cost a LOT !
Have a good Day !
S.W.