vehicle stalls after high speeds

What is your question?

i have a 92 cutlass supreme s 3.1 197,000 miles. the car runs good at first it fires right up and goes into gear just fine. but after i take it on the highway or stay at constant speeds over 40mph the car will start to buck when i come to a slow down or come to a stop the car wants to stall out and if you let it stall or turn it off it will start right up but when you put it in gear it will stall out again unless you let it sit for awhile. my check engine light is also on the code coming back is to high of voltage to the map sensor for 4.8 seconds not sure what this means either. any help or advice is appreciated