1995 Chevy Blazer engine wont start

I have a 95 blazer with 159000 miles. I recently rebuilt the motor it only has 33 miles on. I was driving it one day and it just died. I was able to get it started but had to hold the pedal to the floor and was able to get it home. I went to pull it into the garage and it died again, this time with no luck in starting it. I have checked fuel pressure and is about 58 to 64 psi key on and can see the regulator relieve pressure on the gauge. I seperated the intake and checked the poppets the are allowing fuel out of them. I have checked for spark and have spark on all six plugs. I am a fairly good mechanic but am at a total loss on this one. I also drained all the fuel and put 10 gal. Of fresh fuel. I have gotten where it tries to start but to no avail.