When I'm driving on the highway in 4th gear the speedometer jumps around like crazy reading anywhere from 30-50mph and the trans will down shift back and forth from 3rd to 4th.

The trans is a 4L60e that has no known problems. I did a search and could not find anything like this, hope you guys have some answers.

Also, could this be causing a misfire if I was driving it hard in the lower gears. The reason i ask is because i was getting it dyno tuned and the tuner was complaining about the speedo moving around and there was also a bad misfire after 4K.

Thanks!

 

check the vehicle speed sensor (VSS) maybe it's faulty & trans fluid is getting into it...also the connector/wires...

 

I have another tread open on ls1tech and after digging around with a tech II and multimeter we found that the connector was bad.

I'm waiting on a new pigtail to come in the mail Monday and hopefully that works.

Thanks for your input. You were dead on.