1996 Mustang GT automatic trans slippage - need advice

Hi all,

I'm driving my dad's Mustang and noticed something. From a stop, if
you romp on the throttle (say, 75% or more throttle angle), when the
trans does a 1-2 shift there's a loud "SCREEE!" and the definite feel
of trans slippage.

Is this a common indicator that the trans is ready to go? It has 125k
miles on it and has seen regular maintenance.

Is there something I can do to it in the interim until I have the $ for
a rebuilt trans?

Could this possibly be the torque converter?

I'm thinking using an ATF with a high static coefficient of friction
(Trick Shift, etc.) would help, IF it's trans slippage. Any comments?

.