Why does my truck turn off when I put it into Drive or Reverse? on 1993 Chevrolet 1500 Pickup

"I own a 93' chevy silverado, & the problem is, my truck turns on fine but then when i try to put in into Reverse and press the gas it turns off, & tried it with Drive but it does the same thing. Can it have something to do with transmission?" I had a mechanic look at it and he unpluged something close to where the oil pan is, and now it drives fine. What could be the problem?

the sensor costs about 30-40 buks.. it should be located on the front of the valvebody..
What is this sensor called? Transmission sensor? All help would be appreciated, thank you very much.
2 more answers , 2 more comments
torque converter lock up/ he disconnected the conveter. you can do that on the old trans. i am surprised he did not tell you. this is temporary. with it disconnected there is no lubrication to the main shaft. this will fail the trans in a short period of time.

Thanks i am gonna check it out
my 1993 chvey subabun has the same probblem i turn it on and it idles fine but whe i put in drive it will turn off unless i keep pressing the gas
Any luck with figuring out the problem? I'm having the same issue with my 93 Sierra pick up.