thanks for the help but it turns out A. I'm an idiot and B. I had a weird string of luck.
the tropius is fine, what happened was I encountered some zigzagoons and poochenyas with -speed personalities a few times in a row. I tested with him some more and it started to work most of the time again, then the next time it didn't I caught the pokemon and it had a negative speed personality. It's just weird I hadn't encountered that on any of the other ones then this tropius had it happen several times in a row. since theyre such a low level that 1 or 2 point difference in the stats completely changes the outcome.