My Gen.2 -Now only holds 31/2 gallons of gas in the tank bladder

I suspect the problem with pressurizing the bladder to expand it is that it can break some connection inside the tank. The bladder itself may or may not be able to expand more after this treatment, but if one of the fittings to the bladder now leaks it isn't a win.

This bladder tank brings to mind the pistons used in thermodynamics class - perfect seal, frictionless, massless. I can just picture some Toyota engineer mulling a gas tank with an equivalently unobtainable large flat piston sitting on top of the gas in a steel tank, moving up and down as it fills and empties, never allowing a gas pocket to form on top. One moving part, almost no evaporation. Minor problem - impossible to make that way. Then maybe they thought, let's put a bladder in the tank and keep it pumped up to fill that air space. Complicated thing keeping that filled properly, but the tank would otherwise have been completely conventional. In retrospect, it would likely have been many fewer parts, but prone to failure when the pressure regulation mechanism broke or glitched. Then they had an insight, let's put the gas in the bladder, all we need is a few tubes and valves! Clearly one of those situations where the lack of a manager willing to to enforce KISS let things get out of hand.