Not wanting to run.

I have a 1999 Jeep Grand Cherokee Lerado Straight 6. I can start it and drive about 3 blocks and then it looses all power. No matter how much gas you give it won't go. You can hear like a back fire through the air filter area.It does it with no signs. No check engine light had came on. I have replaced the fuel pump and socks, fuel filter, crankshaft position sensor, changed plugs, and catalatic convertor. Nothing has worked. Please help