Backfiring at mid speed

[plriley]

I have a 1999 4.3L that seems to be running OK. It idles well, At WOT it runs smooth - it does seem to be mildly underpowered but runs well -, going slow it is smooth. The problem is at mid speed - around 20-25 mph - it is backfiring a fair amount.

Any ideas?

Once in a while when you punch it at idle it coughs and sputters a bit, but the main problem is the backfiring. If it was running lean I would think that at WOT it would have trouble as well.

I am stumped.

Thanks

 

[alldodge]

Don't know which motor, but if it has a Holley carb its probably the power valve