My well pressure tank is set at 40 psi the pump goes on at 42 psi and goes off at 64 psi. I check this several times running the water. Interesting thing is as the tank charges it's slow from 40 to 50 as you would expect, then rockets up from 50 to 65 then crashes to 50ish and sinks slowly back down to 40 where the pump again comes on. All while the water is running. If I shut the water quickly at 65 it stays at 65 so there are no leaks. What is going on??

Assuming you have a bladder tank. I suspect that you have a ruptured or leaking bladder. With tank under max pressure let the all the air out the schrader valve. If you get water out the schrader valve you have a ruptured bladder.

OR

Turn the pump off, open a faucet somewhere, open the drain valve and drain the tank. Then recharge the tank to 40 psi and turn the pump back on. See what happens.