Silverado stalling at stop and in reverse.

I have a 1993 Silverado 1500. It's just
over 100,000 miles. Recently it's been
stalling when I'm idling at a stop light or
sometimes if I put it in reverse. It only
happens when the engine warms up, not
when it's cold. I can go a few miles
without it stalling at idle but as soon as it
warms up it begins. After it warms up I
have to put it in park and rev the engine
then quickly put it in drive when the traffic
light changes so I it doesn't die out. It's a
hassle but I hesitate to take it to the shop
becaude I don't want them to cheat me,
I've had some bad experiences with
mechanics sabotaging my other car. At
least it's running. It's been a great truck
and never given me any problems just the
usual maintenance upkeep. Any ideas
would be very much appreciated. Thanks