Hi, I'm pretty sure its not major at all but, what happens is while driving, such as starting off, Going into 2nd gear -Automatic- from 1st, it gets a very subtle period like 1 to 1.5 seconds where right after it shifts it sorta is in neutral but not fully. It only seem to do this when its warm. Although about a month ago i had to replace the TPS because the Tranny wouldn't stick with a gear and it was stuck at around 1500 rpms, and would go into overdrive. And mainly it would stay around 1st 2nd and 3rd. But i had to manually shift it myself. so i think while it kept switching from 1st to 2nd and vice-versa, its causing this.
-Thanks

 

check these out

FYI 4L60E common problems / failures | GM Truck Headquarters

 

great posting!!

 

One thing that is not recogmended is manualy shifting with the problems you have with your tranny.It will do more serious damage to the trans by doing this.