The Crown Victoria is a great car! I had one, but if it wasn't for the gas guzzling 4.8 V8 engine, I'd keep it.
It's true you can find a Crown Vic (P71) more easily. Craigslist is a great site to find that cop car you're looking for.
I have a 9c1 Impala, and the tranny was slipping and I changed the fluid; they have a tranny filter. If I change the tranny filter, will it help it? I love my car and I don't have the money to rip the tranny out.
I would suggest the following:
1. Install a trans-go shift kit for the 4T65-E transmission - you must remove the pan and filter (21 bolts, but easy to get to).
2. While the pan is off, change the filter, clean the magnet on the pan, and wipe off clutch dust from any visible parts (looks like a grey or black powder or goo covering most of the parts).
3. Go to Valvoline, a service garage or anywhere that does a transmission flush, and have it flushed (dropping the pan only removes 30%~50% of the fluid, as most sits in torque converter).
I have an 01 9C1 Impala, and the tranny is shifting better now at 142k miles than when I first got it with 96k, after doing a general maintenance overhaul. I would suggest also having coolant flushed(every 30~60k if you're not using dex-cool), fuel filter, plugs and wires and air filter. Keep up on your maintenance, and you can most likely avoid major failures for the life of the car.
Also for those with subframe popping issues, there is a shim kit for the rear bushings for 2000. For 2001, there is a glue kit for the welds. At least according to GM, those were the fixes for those two years with that issue. Intermediate steering column fix is just lubrication, there is a kit for that too. Call the dealer or Google these problems, and you'll find more details.