It is possible if the selector doesn't lock in to position. Also check the Transmission Fluid level. Low fluid will also be a factor. There could also be other issues that should be looked at by a professional, reliable transmission shop.
It might be the transmission range selector
According to my Chilton's Auto Repair Manual : For a 1989 Mercury Sable : ( 16.0 U.S. gallons , or the optional extended range tank which is 18.6 )
I have a 2001 mercury sable LS premium DOHC 24V engine and usually around 70 I'm at 2500-3000 RPM's
What about it? It's impossible to provide and answer if you don't ask a complete question.
According to my Chilton's Auto Repair Manual : For a 1990 Mercury Sable : ( 16.0 U.S. gallons or the optional extended range tank which is 18.6 )
Depending on which engine you have, an alternator could range from $140-195 (USD) at Autozone.com.
Trouble code P1336 means: Crankshaft/Camshaft Sensor Range/Performance
$250 to $350 range. get it fixed before it messes up the ac compressor and now you're looking at the $600 to +$1000 range
On the transmission selector you put your shifter in neutral position and then you can move the transfer case selector to high or low.
You replace.
Red = gules black = sable within the colour range of heraldry.
RF refers to 'radio frequency'. A selector switch would select a different range of radio frequencies at each of its positions. RF selector switches would be found on short wave receivers and transmitters.