Hi my engine started to idle lower, when i first got my truck it idled at 2,000 rpm when cold and 1,500 when warm, now its idles at 1,000 when its warm and it feels weak and turning my engine off.... what could be the problem? should i just rejust the timing?

Also it tends to give a skip for like sec every 15 secs with drops the 1,000 rpm to 500 rpm, someone told me it could be my muffler what do you guys think?

 

definitely not muffler..

I'd say check the pipe between VAFM and throttle body for any cracks or any leaks. make sure it is tight and sealed. how many miles?