I just got a 06 Impala SS with 20,000mi, I changed oil and trans fluid+filter. I used mobil 1 multi-vehicle atf for trans and (after I changed) I noticed that GM calls for dexron-v1. Do I need to change fluid or will m1 work??? if it will work which is better??? I can not find any info on m1 bottle stateing that it meets dexron-v1 spec. I have only driven about 100mi since.
Any info would help. Thanks

I would suggest you get a complete flush out and the right fluid put back in it.
The multi vehicle fluid fluid is a rip off and may damage your transmission clutches and converter lockup clutch.
There is no such thing as a one fluid fit all.
Good Luck
MT