Miller Rabin - Error probability of .5 a possibility?
The problem is that you got the algorithm wrong.  You use it to generate an integer (which is one of 1, $x-1$, or $y^{x-1} \bmod x$, and then say "prime" if that integer is prime.

That's not correct; in fact, the three integers you list (90007 91571 94343) are each prime, and Miller Rabin should always return prime when given a prime.

Instead, the correct implementation of MR should:


if the initial computation is $y^{(x-1)/2^u}$ is 1 or $x-1$, conclude probably prime.
do $u-1$ square operations, if the result of any of them is $x-1$, conclude probably prime, if it is 1, conclude "composite"
if, after the $u-1$ square operations, you never hit $x-1$, conclude "composite"