I have a recently rebuilt 700r4 with a tci lock up kit for the converter. It will shift through all the gears fine at normal speeds but when it shifts into 4th it will only stay for 5 to ten seconds at a time then slip into 3rd then back to 4th and so on. Iv tried adjusting the tv cable and that hasn`t help. I don`t think its the the converter because i have a switch in the car to lock it up and that works fine. Any advice or thoughts would be great

there are three things holding in fourth gear. the 2-4 band, the forward clutches, and the 3-4 clutches.
is the trans hunting shifts, or slipping into 4th all the time?
if it is hunting it may need a governor reprogramming kit. it can tailor the shifts a little later so that the trans will be in fourth at a later rpm.
B&M sells it-it's about $35. and is called a governor recalibration kit.
if it's slipping in and out the band might not be stopping the reverse input drum from spinning, or the 3-4 clutches might be going bad. Checked the fluid level and condition?
there is also a better t.v. plunger to make fourth stay in gear with more throttle. it is made by sonnax. it goes in the valve body and doesn't require removing the valve body. all you do is remove a roll pin and pull the old plunger and sleeve out.
it's all in the details-but usually costs money eh?