Sorry for the long post, I hope it makes sense.
Its hard to tell what problem you have, you used the term "lock-up" that term is normally used for the torque convertor which only locks up in O/D, or 3rd if O/D is cancelled with O/D button. T/C lock up is mainly influenced by the TP sensor. If TP is out of adjustment "low" it will lock the T/C sooner/lower MPH, if its out of adjustment "high" it will lock the covertor up late/higher MPH. If the upshifts (1st-3rd) are too soon or happen too quickly then the T/V cable may need to be tightened.
There is a white clip on the T/V cable housing where it mounts to the cable bracket, that clip needs to be pried up or off, this allows the cable housing to slide in/out to adjust the slack of the cable. If there is not a white clip then you have a black plastic button that is almost square shaped that needs to be pushed in to adjust the cable.
T/V cable adjustment is pretty critical for proper trans pressures and if the cable is loose it could allow the clutches to slip. What you want is to have the T/V cable a little on the tight side. The purpose of the T/V cable is not to set shift points but this side effect is the easiest to use for proper setup. Its is better to be a little tight allowing the trans to "hold" gears a little longer during acceleration.
To adjust T/V cable, release lock clip or push button, then:
Move the cable housing back (away from throttle body) will increase T/V pressure or raise shift points, side affects can also create sensitive downshifts and harsh engagements. Too tight can also cause upshifts to occur to high in RPM range, or the feeling that its stuck in a lower gear and will not upshift. Thats when you know you went too far.
Move the cable forward (toward throttle body) will lower T/V pressure or lower shift points, side affects can be early/quick upshifts, or excessive throttle to make downshifts, slip/shuttle shifts, and slipping trans on accel. If its too loose it will seem like the transmission is shifting into higher gears too soon while you are accelerating, this is when you know its too loose.
95 ZJ 4.0L 42RE, 231, 3.5" lift 31" KM2's
"Dont let out until its too late"