I bought a 1991 Caprice Station Wagon with 70,000. The car appears mint. Everything works, and the only thing I noticed is that when going from 30-40 mph, there sometimes appears to be a hard shift, that is I can feel the transfer to another gear. I received no service records and was wondering what service I should have done to ensure the car lasts a long time. Thank you.
Change the automatic transmission fluid and filter. Some recommend adding Auto RX to the transmission.
Replace everything rubber (belts, hoses) under the hood if it appears to be original, or 10 plus years old.
Replace ALL fluids.
Clean (internally) the egr valve, the iac (idle air control) valve, the throttle body and throttle plate, and the MAF (Mass Air Flow) Sensor.
This is a start.
Besides what hellokit suggested, I also replaced the plugs, wires, and distributor cap on my 93 Caprice when I got it in 2002. It was my Father-in-Law’s, so I knew the history. I had a Motovac fuel system service done by my trusted mechanic when I got it.
The 700R4 shifting is controlled by the Throttle Valve (TV) cable. My Caprice has always shifted firmly, but not abruptly. Recently the TV cable needed adjustment because the transmission was hanging up in first and then shifting violently into second gear. The adjustment has to be done in very small increments, it only took about 1/16" to return the shift points to normal on my Caprice. Unless your Caprice is hanging up in gear and shifting violently, I would leave it alone.
Thank you for the kind responses, I will take your advice