I have a 2002 LS 4wd. When driving at speeds of at least 45, the car will jerk/jump a little. The first time it did this I was at 60mph. To make sure I wasn't steping on the gas pedal, I set the cruise control. This assured me it wasn't my foot slipping of the gas my looking at the RPM's bouncing. I can feel just a slight jerk....when it does this, the RPM's will bounce up (just a tad) then RPM's will go back down. Check engine light hasn't come on. Does anyone have any ideas what this is? Is it serious? How much to fix? Thanks!

First pull your trouble codes just to see if the computer is seeing it.

also check the trans fluid, you said the rpms go up but didn't say anything about speed so assuming it did not go up...sounds as if maybe trans is slipping...lack of fluid or other problem