engine stalls when put into gear (autotrans)

hello, i have a question that i was hoping someone could assist me with. i have a 1990 gmc sierra pickup 1500 with a 5.7 350 engine and automatic transmission. i have not ran the engine for appox. 1 week and now that i have tried to run the engine it will not move. it runs a little rough anyway do in part i am sure to the 300,000 + miles that i have put on it. it stalls out when i put it in gear. it has been rather cold outside and i dont park in a garage so it is exposed as it were to the whims of mother nature. i am just fishing for suggestions. if someone else has allready gone through the painstaking process of eliminating possible fixes and have found one that works, i'll try that first. i do appreciate any attention that anyone will give this problem of mine. thank you much . alan

First thing to check is fuel pressure. You may have had some water in the gas and it iced up in the fuel line. Throw a bottle (or two) of DryGas in the tank and then try to start it in the warmest part of the day.

//2000CAYukon