Wrong way around Wren....he'* got a 1995....he put in a 1993 trans.
Ok, here is the thing (and I am going on memory, so don't hold anything I say as gospel, but rather as guide). Most of the solenoid pinouts changed for model year 1994, and the addition of the trans temp sensor. The 1993 trans you put in would only have a temp switch, not a sender....and only if it had traction control. You putting in a resistor where the sender *should* be is throwing off the PCM, as it expects to see a variance in temp, and not a constant. And from your description of the way it goes in and out of overdrive, I bet you that resistor you put in corresponds to the resistance given when the trans is running hot.
Another question....what gear ratio is that 93 trans? Is it the same ratio as what you put in?
You will find that 1993 trans to be a pain in your side until you either properly modify the transmission internal wiring to match the 1995 trans, or rearrange the pinouts externally and add a sender to the circuit. Either proposition requires work and patience.
Welcome, downwardly mobile yuppies, to the dawn of the Age of Nefarious.
1993 SSEi - FrankenJinx - dead and gone.
1994 SSE (136K strong) - 180* t-stat,HD alternator, most unequipped SSE on the club, XM radio, Kenwood CD/MP3.
2006 Chevy Malibu Maxx LTZ - Custom 2.25" manifold-back exhaust w/FM-80. Probably the only Maxx with this system.