Cadillac Repair: 1991 Cadillac DeVille {152,500 miles on the car}, gasket leaks, combustion chambers

Question
I have had a new fuel filter & spark plugs replaced on my Cadillac within the past three weeks due to sputtering and stalling that the car was experiencing. In the past couple of the days the car has begun to shake when I start it, and continues to shake while driving, and I experience the most shaking when the car is stopped at a light or stop sign. There is also white smoke coming from the muffler. I smelled the smoke coming out of the muffler & it smells like gas. I found out when I got my spark plugs changed that there was a leak in my water pump. I really just want to know what the true problem is & if I can afford to even fix it! Thank you!

Answer
WHITE smoke from the exhaust is caused by anti-freeze getting into the combustion chambers.

BLACK smoke from the exhaust is caused by excessive fuel getting into the combustion chambers.

This engine is very very prone to having head gasket leaks where anti-freeze is getting into the combustion chambers due to stripped engine block head bolt threads .