Automatic Transmission problems of the 2003 Kia Motor Optima

After stopping at a stop sign I tried to accelerate and turn left. My car would not "go". So I pressed the accelerator harder and it finally and slowly moved forward. I have an automatic transmission, but it was like I was driving a manual and had tried to start in 3rd gear instead of 1st. It's almost like my car had to catch up for a minute before it would go. It has happened several times since that to different degrees. It is a 2003 with only 41,000 miles and no longer under warranty since I bought it used. I am afraid it will do this on the interstate or when I am trying to merge and could be dangerous.

I was driving my 2003 kia Optima on i85 at 65 mph when the vehicle suddenly lost power and slowed quickly to less than 10 mph. The vehicle continued to sputter and backfire until I was forced to pull over and wait approximately. 15 minutes before proceeding normally. My wife has also experienced the same problems and is afraid of being involved in an accident. The vehicle has been in the shop for this issue 4 times. The last repair involved paramount kia in hickory where the mechanic replaced many of the assumed problem parts such as faulty wiring harness, ecm, maf sensor and fuel pump without resolve. The service department stated that they had no idea on how to fix the problem.