2000 Chevy Astro 2000 chevey Astro rear drive. Stall inte

2000 Chevy Astro 6 cyl Automatic 150000 miles

This has been going on for several weeks. I've had it to the shop they can't find out what is wrong. We drive it for awhile and it just stalls. Sometimes it will restart and we can go on down the road and sometimes we have to wait several hours before it will restart. At times when it restarts it will go 1 or 2 blocks other times it will go miles. I've changed the fuel pump, fuel pump sensor, fuel injectors, and a cracked vacuum line I found and an alternator. Still have the problem. Any idea's on what I am missing. My wife is handicapped and we really need this vehicle to run.