Hello I have a 93 gmc 4x4 1ton 7.4 with a 4l80e and my lock up convertor locks up intermitily while at cruising speeds 65 70. I will be going along and it will lockup and unlock for a split second. Any idea how to trouble shoot this to figure out what is causeing this. Other wise the trans works like it should.

Most likely valve body wear.

http://www.sonnax.com/announcements/34994-01K.pdf

//2000CAYukon

Is there any way you coyuld give me more info on this? and if you can can u explain it to me please and thank you. went to website thanks

The pcm controls the application of the tcc based on tps, speed and engine load inputs, the valve body issue may not apply to your year. A full scan will look at whether the listed functions are within operating range, an improperly adjusted stop lite switch could cause this also.