My truck kind of does this too. I will be driving easy, try to keep rpms around 1500 before the trans shifts to the next gear. Around 35, it will shift into 3rd then lockup then unlock and stay that way until about 38-42 then lock into 4th and lock up. Also, my truck will go in and out of lockup at highway speeds. I almost have to keep my foot down(accelerating) to keep the tc locked. it gets really annoying and its eating up my gas mileage. The trans just had a rebuild about 20,000miles ago with a shift kit. Any thoughts? Sorry for hijacking, I didn't see then need to start a new thread when this one was already here.

 

On a side note, yesterday when I was driving on the highway and my trans started leaking fuel out of the breather valve bc the trans is overheating. I took it to the shop and that is what they said. He said that the TC wouldn't lock up either. Any thoughts on what to do?

 

I'm going to move your posts into a thread of your own instead of potentially pulling sifd4x4's thread away from his problem.

A clogged transmission cooler will cause the trans to puke fluid out of the breather.