2008 ford ranger, automatic transmission with 65,000 miles. Started having a major issue with the truck not wanting to move when in Drive. Was suggested to me to add and I did ad some automatic transmission 'conditioning fluid". Almost immediately the truck had no issues and I thought I had corrected the problem. Now, about 100 miles after adding that fluid the transmission is acting worse than before. The truck needs to be revved up in Drive before it will move forward and then it moves off very slow. Same thing happening in reverse. No sounds or vibrations coming from the vehicle. The transmission fluid level is and has been in the normal range. The fluid has not been changed for a few years. Any ideas from anyone? Trying to avoid my local mechanic as his expertise in my small town is not transmissions. Thanks