2003 3600 V6 Shifting issues

My bad my Impala is a 3800 or 3.8 Litre not a 3.6

I have a 2003 LS with a 3800 V6 that is having major shifting issues. I had the cruise set at 70 mph as usual and watched my tach jump between 2 and 3 for a while till I downshifted and then put back into proper gear. Also when climbing hill or heavy excelleration it will tach at 3 or 4 but not gain speed very fast.

I tried to check timing but can not locate the timing marks.



Any help.

Should have known better. Have never had anything but probs with V6 motors.

Just changed the Transmission fluid and filter. after initial test drive still shifting funny.

I am thinking maybe a vaccum problem. Could this be the issue?

COuld really use some help with this.

This needs to be scanned with a trans function scanner there could be an issue with one of the shift solenoids, you cannot time this engine it has all electronic controls. Your description points to a tran issue, but someone familiar with these symptoms should road test it, there are other performance related possibilities.