1992 Cadillac Deville

Hi l know I asked a question last time and I was told to get a fuel pressure gauge. I have not had time to but now the car is getting worse. It is a 1992 Cadillac Deville. When I take a turn turning the wheel to the right the car acts like it is not getting any gas. When I finish the turn the car will not accelerate. I have to put my foot all the way down to the floor and after 3-5 seconds it kicks in and takes off. The car does not die it just acts like it does. It only happens with 5 or less gallons in the car. Today I changed the filter it was working a little better the reason I changed it was because I was going 60 on the highway and when I floor it it acts like it was hesitating it would not take off. So now after I changed it it did all right. Now when I come to a stop light it dies I have to put it in park and restart it. It takes a few seconds before it starts. I am not sure what is going on. Any ideas. I was wondering if it could be the fuel pump because it has never been changed but I need to buy a fuel pressure gauge and I guess start their. Any suggestions. Thanks. Off it has a full tank of gas all the way to 6 gallons it does not act up. It only happens when I hit 5 gallons.