I have a 2003 wrx with 159k.

I bought the car with bad synchros but other than that drove fine. Had someone put my new trans in (dumb choice) and ever since I’ve had a sputter. I will say they left my o2 sensor wire hanging on my exhaust and it melted. I also notice I have low vaccum so I’ll be smoke testing when time let’s me address that. I’ve replaced pump and filter (not injectors) I’ve cleaned my maf. The oddball thing to me is when I drive it after I cut it off and back on it has a 50/50 chance of running very rough and not wanting to move. If I cut it off and back on sometimes it fixes it for the whole ride home sometimes just for a couple mins. I’m wondering if that could be from the possible vaccum leak or if it’s looking like an electrical issue? Please and ty🙏