Ok, yesterday on my way home my blazer started to bog down, it wouldnt go when I pressed the gas, when I put the truck in park and pressed the gas it would rev fine, then once I put it in drive it wouldnt go over 30MPH and it would back fire.
We thought it was the fuel filter, changed that, still sputtering.
Any thoughts? Open to suggestions.

Thanks

 

Sounds suspiciously like a catalytic converter failure. If you hit the catalytic converter with a rubber mallet, does it sound like stuff is rattling around inside?

 

I recently bought a '95 Blazer that was in excellent shape but had a serious backfiring problem. To the extent it had made the oval shaped muffler into a big round muffler with the inlet end blown open. The previous owner claimed to have put new tune up components, plugs, wires, filters, etc. in and from the looks of everything he had. I noticed that it ran semi- OK when it was cold or at steady highway speed. In town, after it had warmed up, it would barely run. That reminded of a problem on another car that exhibited the same symptoms. I replaced the ignition control module and it fixed the problem. Judging solely from looks it was very likely to have been the original.

This may not fit all of your symptoms but the backfiring can be caused by the cylinder getting a shot of gas and not getting fired on and passing the rich mixture into the exhaust where it eventually finds an ignition source.

 

This does sound a lot like when my cat converter substrate broke up and clogged my exhaust. I didn't have backfiring though.

In park the engine would seem fine and rev appropriately but in drive up to a certain throttle position it would have almost no power and going WOT resulted in the engine revving up high but no acceleration, almost like the torque converter had failed.

Replaced the cat and minus a few bits of catalyst substrate still in the muffler, it runs great.

Also, when I was driving it with the cat clogged like that a hummer probably had better mileage than I did. Figure a quarter tank of gas or more for a drive across town and back ~25mi total.