Cadillac Repair: 1991 cadillac sadan deville trans, sadan, modulator

Question
Hi I have a 91 sedan deville 4.9 that won't shift into low automatically I can shift it manually and it works fine.im thinking maybe trans vacuume modulator. What do you think? I thanks your input. Tim

Answer
Are you ABSOLUTELY POSITIVE that you are starting out in FIRST gear ?. Is it possible that you are starting out in SECOND gear ?.

Try starting out in DRIVE and at about 5 miles per hour, Manually shift into FIRST gear and see if the trans downshifts into FIRST.

As to modulator fault. NO.

IS or HAS the CHECK ENGINE light ever illuminated while driving the vehicle and or has any other lights illuminated or any messages from the message display center ?.

What work or diagnostics of ANYKIND WHAT-SO-EVER have been performed on the vehicle trying to fix this problem ?.