I've read about 20 or so threads looking for something matching. Some were similar but nothing exact so I need to ask specifically about mine.
I have a '99 3500 4x4 V10 with 60,000mls. It has a rough idle and no power on acceleration, sometimes. It can happen when engine is cold or hot, never on startup. It disappears when I floor the accelerator.
This is what happens. I'm at a stop for a minute or longer, it starts idling rough, doesn't die, I give it the gas and I feel that it has no power, I give it more gas, half pedal and it's like it is idling through the gears, no power. I put the pedal on the floor and let off and the power is back, runs normal, idles smooth.
Sometimes I will let it accelerate with no power, not putting the pedal to the floor, and it will clear up itself with a pop sound coming from the left side of the engine. It's not a traditional backfire, loud from the back, it's a mild pop, just one pop, and the engine runs good.
This problem doesn't happen every time I drive it. I'd say it happens about 80% of the start cycles. It can happen multiple times in the same trip as well, hot and cold.
Any ideas?

 

when was the last time a tune up was done? sounds like its misfirng. however, could be a clogged cat too.

 

or bad tps.....