I have a V-6 Dodge 1500 .

it was running a little rough so I changed the spark plugs .

it ran better.

I must have mixed up four of the six wires a few days later.

I didn't hear knocking noise so I thought it was alright.

It was alright at first, I don't know how long I drove it, but then it started running like crap .

​​​​​​It was backfiring so bad and smoke out the exhaust.

I had to floor the gas pedal to keep it from stalling.
Even at 70 mph it was running like crap trying to stall.

At stops or slow speeds I had to hold the gas to about 1500 rpm's to keep it from stalling

So, spark plug change cost me about $50 all together, because I got a second set thinking I might try new ones and see if it fixed it,
but it was wires on wrong plugs

 

The spark plug wires need to be installed to support the correct firing order. Wires installed incorrectly can certainly cause some of the issues you're experiencing. Ensure the spark plug wires are installed correctly before doing anything else and see what effect that has on the motor.

 

What plugs did you install? Plain copper plugs work best.