Backfiring Suburban

I have a 92 Suburban and can not figure out what is making it backfire, So far the egnition module, distributor, power coil and computer have all been changed. The timing was rest this afternoon, but it is still backfiring. The last tuneup was about a year ago. Anyone have anymore ides for me to try

Thanks for your help

Wendy

When does it backfire? Where is the fire come from? intake or exhaust?

under what circumstance? like temp,rpm,load,throttle position,ect.

The backfiring is mostly when I try to speed up for highway driving. I am not to sure where it is coming from. I can feel it under my feet as I am driving. The next thing we are going to look at is vacuum and exahust leaks. Not sure what we will look for after that.

without seeing/hearing it or having any other info. I am going to guess a camshaft, second choice is a valve.