... It seems like Met from one particular manufacturer gives me serious GI problems, where some of the other generics work fine. Normally I have a stomach that can take anything. I found my kryptonite and it's made by Matrix Labs. Any others find problems like this?

I've been taking 500 BID for a couple of years. I know of two brands from the VA that have worked fine.

The Matrix Lab version came from a local drug store. Usually by the second dose, my whole GI tract is talking to me.