1994 Chevrolet Cheyenne idle high, doesn't down shift

You may need to check for a vacuum leak? If you fully obd1, check for applicable trouble codes. You should be able to check those codes, yourself. If 12 pin datalink connector, you use a jumper wire at the A & B terminals on connector, usually lower right side of dash for the connector. With jumper wire connected, turn key just till dash lights come on, no further, then the mil on the dash starts flashing, you count the flashes to get the codes. Your looking for two digit codes.

How long since a tune-up? Also, check the idle air system and make sure the throttle is closed. Engine idling, block off mouth of throttle-body, should be a big effect on the idle, it should kill the engine. If no effect, your getting false air from somewhere.

I'm sorry on the connector location, under driver side of dash. I'm still working on my first cup of coffee.