I have had a 4l80e in my ta for several yrs now. It has shift kit and better clutches with a huge bar and plate cooler. So one day I drove the car to work ran fine shifted like always temp normal. After when I went out to go to lunch I put car in reverse and nothing happened gave some throttle and still nothing so I pulled forward and drove down street. I noticed car was not going into overdrive. I then set my scan gauge to gear position and drove again. What I noticed was 1st worked like normal 2nd like normal then when gauge showed 3rd it was still in 2nd then when 4th was commanded it went into 3rd which I confirmed by speed and rpm still no 4th gear. Trans temp normal fluid color smell and level all normal. Any ideas I'm baffled? All solenoids tested ok via snap on scanner. Could valve body be the problem?

 

You're 3rd gear clutches are failed, what you think is 3rd is 2nd gear overdriven.

 

Ok so 3rd is related to reverse how exactly? I'm just trying to understand how it all works, thanks.

 

3rd gear clutches are also used to make reverse.

 

Is there anything I could have done to make it last longer next time? I'm only making about 600hp or so and I thought my build was plenty strong given all performance parts that are in my 4l80e.

 

3rd gear is the weak clutch on a 4L80E when using a stock or near stock valve body. I don't know what all you have done to it. What we do to the 3rd circuit is one of the key ingredients to our builds.
I've stated it here many times, a stock 4L80E is only good for ~450-500 HP before the directs will fail. They won't fail immediately, but they will fail over time.

 

It has the transgo hd2 shift kit with upgraded clutches but then again it lasted for 4 years .