i having a problem with the tranny slipping, it wont catch any gears i have swaped out the transmisson once already but still doing the same thing.

a machanice said it could be some wire running from the transmisson to the computer but i have no idea what that is.
anyone know what the name of that wire is or what might be the problem

 

There are two shaft sensors, one on the backside another on the front, the speed sensor, located under the TB, and the shift solenoids.
Being that both transmissions exhibit the same problem, and the replacement is a known good one, you may want to look into the TCU as possibly being fautly.

Make sure the transmission ground wire is connected. From the Negative battery cabling there will be a heavy gauge wire that bolts onto a tab near the dipstick. Check shift solenoids by unhooking the green connectors and running a jumper wire from the Positive side of the battery to the each connection. The solenoids should click.

Verify that the cable leading down from the TB is correctly adjusted.
It should have no slack in it. Once the TB begins to open the TV cable should move on the side of the transmission. Check this after the engine has been warmed up.

When you replaced the transmission you also replaced the torque converter correct?

You should never reuse a torque converter from a bad transmission. It may be damaged and contain particles of metal and friction material from the damaged transmission.