I have a 2000 4.3L engine and I replace the timing chaine, rings, rod & Maine bearings.. now I have 150 on compression, it fires, 65 psi on fuel. It back fire one time and it make a noise like it pumping. I set the cam at 6 & crank at 12 on chaine . I set The dis on the 6 mark after turning the crank too the marks no start

 

Distributor timing is probably off. Maybe 180 degrees off.

 

Maybe crankshaft positioning sensor? That was my issue I had forgot to install it back after rebuild. Good Luck