I have a 96 Mercury Grand Marquis. The car lurches while driving feeling like it will conk out. Usually when going uphill on the highway and trying to accelerate or maintain speed. This does not happen all the time and usually starts after drving about 30 minutes, but sometimes it happens after drving just few minutes.Then it will do it when slowing down or stopping and trying to accelerate. We just had the right catalytic converter replaced. It ran great for 1 day then started doing it again. My husband replaced the fuel filter put in some gas treatment, and made sure all other fluids were full(oil, transmission fluid,ect). Again it ran great for 1 day then started again today on my way to work. What else could the problem be? Someone at work suggested it may be the fuel pump. What do you think? and how much would that cost to replace?

I have a 96 Grand Marquis with a similar problem. Also on the highway it would just conk out on me suddenly, almost felt like I was hitting the brakes, then it would pick up again. Eventually got to the point where it was stalling out on the highway and at red lights. One day it wouldn't start. Mechanic said the fuel filter was clogged solid. It has run well but every once in awhile still stalls out on me. From talking with other Grand Marquis owners and the mechanic the Mass Air Flow sensor may be to blame. He wanted to charge me $400 but I found the part online for about $85.

Check that the fuel pressure is within spec.
also the EGR port on the 4.6 litre can get full of carbon or the EGR valve does not close fully and simulates a vacuum leak.it can cause rough idle ,poor acceleration .it usually sets off the check engine light ..the lower intake can leak coolant into the combustion chamber and cause issues.