Well, then, you might as well sell it.I understand to do some work and parts upgrade but at this time I am not willing to put any money or effort into it.
It's shown that it is capable of fine accuracy, obviously something is heating up/moving/binding/shifting/etc once you start really shooting the thing. This is not uncommon and I won't bore you with the maudlin details of all the squirrely firearms I've gotten that required some detective work and a few parts to square them away, but to me the effort was worth it. And this is not to say something like this wouldn't happen with the next M1a no matter what make you would get.
If you are frustrated with it, set it aside for a while or sell it. And, as the others mentioned, maybe get another set of eyes on it... you might be staring right at the problem and not see it.