2001 Chevy Express Vehicle Has Hard Starting After Fuel Pump

Other Category problem
2001 Chevy Express V12 Wheel Drive Type unknown Automatic 102000 miles

A couple of months ago, my van (I have a Chevy Express Conversion Van) just totally stalled and died on me. I was told it was my fuel pump, and we had the fuel pump replaced (A $700 job). Since then, I notice the vehicle is very hard to start. It cranks and cranks beforeit actually starts, and the past few weeks it has been getting worse and worse, and some days not starting at all. On the days it did not start, my husband sprayed starter fluid, and then it started. Once started, it will stay running and I'll be able to start and re-start after that. It is usually the initial start of the day, or if it has been not running for a good part of the day. I notice the colder it gets, the worse the problem is. We called the shop where they put in the fuel pump, and they said it sounded like the mass air flow sensor. So we replaced: The mass air flow sensor, plus it has a new battery, and new sparks.
Now today, 1 days after I put in that new mass air flow sensor, it cranked and ckranked again. It did start, but it was very hard starting, and I did not think it was going too.
What else could it be?
Could the new fule pump they put in a few months ago be faulty? I am at such a loss here. Thanks!