Hi welcome to our little spot.
I'm the early bird, so I'll get some questions in.
First where do you need a garage? (city, west, south, east, QC side?)
Now, is the car a 4 cylinder or v-6? Also a bit more detail on it's behaviour. Does it stall completely or just enter a stuttery, shuddering phase under acceleration? Also does it light up the 'Check Engine Light', if so, it should store a code to indicate what the problem is.
The automatic has a fairly common fault. The torque converter clutch (TCC) fails and the symptoms are as follows. After hiway driving the car stalls at a stop and typically will stall again when put into drive. This can be diagnosed by disconecting the TCC to see if the fault disappears. The TCC locks the torque converter on the hiway for better mileage. Driving with it undone won't hurt the car but may lessen mileage. It is inside the tranny case so, it needs to be fixed with the tranny apart.
Other problems are electrical due to heat in the engine compartment. Coils and ignition modules are the main culprit, especially on a v-6. I'm sure we could scare up a known good module to test. If it's bad use a GM (AC Delco) one as they seem to last longer.
Let us know a bit more. BTW, is this the black one in Lanark?
Gary