we have a 2005 Buick lacrosse that is having an occasional issue where it will shutter really hard when starting from a stop. it feels as if it is starting in ine gear then ckunks into first then is normal; or maybe like locked up torque converter then unlock and normal accelleration. any ideas what it could be? last time it happened scanned and no codes.

 

Consider dropping the pan. I had a vib with normal acceleration from a stop as well. I finally dropped the pan and found shiney metal pieces.

https://ls1tech.com/forums/automatic...vibration.html

It's worth a look...if the pan looks good you're only out the cost of new fluid and can look elsewhere.