My 1999 gmc Sierra has been running as if it were runnin low on gas, it...

[Blade Wanihandi]

...drives but only it only get low rpm? And it also sputters and the muffler gets hot and it recently backfires! I had changed the fuel pump, fuel filter, and spark plugs! But nothing has changed it still runs the same. Please help me

 

[Molson02536]

...drives but only it only get low rpm? And it also sputters and the muffler gets hot and it recently backfires! I had changed the fuel pump, fuel filter, and spark plugs! But nothing has changed it still runs the same. Please help me

You could have a Catalytic converter that has gone bad. Take it to a muffler and have them inspect your Catalytic converter. You can do it also but getting under the Sierra and banging on the Converter and listen for any rattles that would indicate the internal parts in the Converter had corroded and is causing a exhaust restriction.

Good luck and keep us posted.