Hello and welcome to Just answer.com, Super mechanic here. About your vehicle.
It sounds like there is a problem with the TCC system. They will do that when they are warmed up, the torque converter clutch will lock and unlock while driving. That will not set a trouble code most times.
What you can do is; When you are driving with the vehicle warmed up and you start to feel the "chuggle" or miss is, just touch the brake pedal, enough to make the brake lights come on but not enough to actually apply the brakes and see if the engine smooths out. If it does then the problem is within the transmission TCC solenoid system. That would be in the torque converter clutch lock up solenoid, the wiring or the torque converter itself , thanks
That fluid is comatable with the Kia SP-lll as long as it is the Dexron-lll
You would want to confirm that the condition is in the TCC system and not a 2-3 upshift slip or flare, as there is an update for the computer software for that concern.
If the trans fliud is up to the recommeded level and there are not TCC concerns, you might want to check the updates with the manufacturer. Here is what the one says that I have in my data base.
Date: Wednesday, June 07, 2006
Area: N. America
Subject2004-2006 Spectra 2.0L 2-3 Shift Shock(Transmission/Driveline - 016)
This bulletin provides information related to a repair for 2004MY through 2006MY Spectra automatic transaxle equipped vehicles with 2.0L CWT engines.
Some Spectra automatic transaxle vehicles may exhibit a second to third gear upshift shock after the vehicle is at operating temperature. This condition may also be felt as a slip or flare followed by a shock while shifting from second to third gear. This bulletin describes the procedure for upgrading the ECU software with new logic to correct the above condition.
The torque converter is the part that connects the engine to the transmission. You wouldn't want to drive it too much if there is any slipping, as that will cause things to wear prematurely.
The best thing that you could do would be to have a reputable transmission shop check for trouble codes and pinpoint the exact problem, or the dealer to see if it needs the update.