No start

Okay guys, you all have been great. I need more help. A mechanic replaced the engine in the car for me. It is a used motor. It was running fine. It did idle a little rough, but nothing alarming. The only issue I saw was the coolant level. Every 3-4 days I was having to top the reservoir off. It was only about an inch below the level. I drive the car less than 40 miles a day. I have only had it back about 3 weeks. Last week on my way home it died as I was driving. It would not restart. I ran the battery down trying to get it to restart. My husband recharged the battery and it started with no problems. I drove it to work the day before yesterday. It drove great on the way to work. On the way home it died again.I was about 4 miles from home, so I had only drove about 12 miles. As it was late they waited until yesterday to get the car home. The car died on them again about about 1/4 mile from home. There is no warning, no lights come on, the thermostat is only half way (like normal). It would not restart right away. After about 15 minutes it did restart. By that time they had pushed it home and were only checking to see if it would restart. Any ideas?

None of the stores around has a fuel pressure gauge. One parts store even told me there was no such thing. It has only stopped on us at night when the weather is cold. How does he preform a load test on the battery? When I asked him about the battery, after it died on me the first time, he told me the battery was good, that I had just drained it from trying to start t and from the lights being on when I was pushed (not towed) to the house.

Ok, they put in a new battery. We still can not find a gauge to check the fuel pressure. It is still doing the same thing. Any other ideas?

The only light on now is the check engine light, but you know how that goes.