Engine rough after spark plug change

I installed new AC DELCO platinum last night.
Since then, my engine gets rough and hesitates in 1000 ~ 2000 rpm in acceleration. TT
Any advice will be appreciated.

Were the wires installed in the correct order? They may be firing wrong. Just a thought....

Did you carefully twist the wire boots before pulling off - maybe you separated a wire internally - seen that one if it came off really hard or with a snap. You have to check the resistance of each wire to see. Is this all you did - as for the order the drivers side is 3-1-5 in the cap front to rear and its marked while pass side is 2-4-6.

I changed one by one. so, It is not possible that I plug in wrong spot.
My car is manual shift. when needle hits around 2000 rpm, it usually turn "shift" lamp on. so, I am using 1000 ~ 2000 rpm a lot.
When I drive in city road with around 40 ~ 50, rpm is usually under 2000.
The most used rpm rage is in trouble. It runs well over 2000 rpm.

Did you put the wires on the plugs one at a time?

Did you change the cap and rotor?
Did you make sure all plug wires were attached properly?
Did you gap the plugs properly?
What year is your truck?

Yes, I put the wires on the plugs one at a time.

Cap & rotor?? you mean distributor??

I think all plug wires were attached properly. but wires are old ones.

I check all the gap with gap gage.

2001 model.

I pulled out each spark plug and ran the engine to see what happen.

I could see the difference each time I pulled out.

But, I am trying to replace the spot with old spark plug where least difference is happening. I will let you know soon.

Did you put the wires on the plugs one at a time?

Did you change the cap and rotor?
Did you make sure all plug wires were attached properly?
Did you gap the plugs properly?
What year is your truck?

There is a distributor cap and rotor you need to replace.

What gap did you set the plugs too?

What AC Delco plug number did you use?

It can also be a cracked plug. The white stuff porcelain. Ceramic looking stuff.

You stated that the plug wires were old. I think I would spend the cash to get a set of AC Delco plug wires and replace them. You may find a huge difference.
Also, you should get a new distributor cap and rotor. Make sure you buy a good quality cap - preferably AC Delco - as the after market caps have caused problems with several of the forum members vehicles. They tend to go bad quickly and you get multiple misfires due to small cracks in the cap.

Thank you for all advices.

Problem solved.
It was defective spark plug.
I took out one new spark plug and installed old spark plug and test-drove.
After several trials, My engine worked smoothly.
I exchanged that defective spark plug and my trucks runs well again.

If I would change spark plug again, I would change 3 plugs first and see how the car runs.

Thanks guys....

You better change you distributor cap and rotor or your truck won't be running smoothly for long.

They have to be changed every 2 years.