700r4 lock-up converter help

[factory2wdblazer's]

dose the lock up have to be hook up on a 1990 700r4 transmission???.... i have drove the truck and it get's all four gear's. but while driveing threw town doing 30-40 when in over drive it seem's like it's sliping while in over drive...is it because iam in town doing 30-40 and in over drive is that to high of a gear for driveing in town??? is it like driveing a stick shift in 5th gear threw town you know how it would be sliping........pretty much i'am confused on the lock up converter deal