Chevy transmission

I have a 1999 Chevy Lumina car. The trans is shifting weird. Sometimes it seems to short shift. Other times it shifts really hard. And other times it seems to not down shift all the way to first gear?? The check engine light comes on. I had it checked out and they said it was a TCC switch. I took it to my mechanic here in town and he said it was more of a mechanical problem, other than being that switch. ( perhaps a sticking valve in the valve body ) He flushed and refilled the trans with new fluid. It’s still doing the same thing. I’m gonna show my age here but… Is there still such a thing as a vaccuum modulator on these cars??

Thanks for any ideas on this matter


What exactly was the code that was set??


Sorry I can’t remeber((( I think it was 74 or 83??? I know this isn’t any help but the guy at Autozone told me it was for the TCC switch. Thanks for the quick reply. I’ll see if I can get another test done on it…