Backfire from exhaust

Hey can anyone help me i have a 2001 dodge Cummins 24 valve and it's backfiring three the exhaust either maintaining speed or deceleration it's a ,6 speed manual please 2 shops have looked at it and they seem to not hear it popping it doesn't matter if it is at running temp or cold someone please give me some suggestions
Thank you

 

Does it do it all the time??? Might do a compression test..... See if you have a bad valve.

 

I can use any assistance with figuring out why my 5.9 Cummins is backfiring from the exhaust sure could use any advice

 

Incomplete combustion, or leaky exhaust valve....... Have a scanner that can read live data? I suspect yer gonna need one.