Agreed on the free scan.

I was a mechanic back in the day and would put my money, based on not seeing it, on a faulty mass air flow sensor. These aren't cheap but can be found at places like pick n pull. It measures the air intake and meters fuel accordingly. The shifting would be due, possibly, to the vacuum modulator on the transmission not getting proper vacuum pressure due to the MAP sensor being inaccurate from inappropriate reading from the MAF.

Again, this is speculation without seeing the car. If you wanna swing by, I'll read the codes.


-Ben-