Vibration in the vehicle

Sir, I have a unique issue. The issue has plagued me through 2 transmission repairmen. It is a vibration that I thought was coming from the transmission and possibly the torque converter. But, to my own investigation and research I found what the problem was. Back to my case the 1st shop promised to fix it and was sure it was the torque converter was possibly cracked. Needless to say after nearly 6-7 months and 3 returns to look into it over and over nothing. I came and got my vehicle and was told I should try AAMCO I to it to AAMCO in Garner, NC. The claimed that they could fix it I gave them the issue as to what was going on and took a ride and was sure it was a transmission issue and in 2-3 days I had my vehicle back and when I got a little ways down the road it continued to do the same thing took it back the next day. The gentleman or manager road with me and said he may need to do some adjustments and should be ready by tomorrow or the next day in this situation. Came to get it and it continued to do the same and he sort of stated that he does not feel what I am feeling although I could tell it was still happening. My last trip was to the GMC Dealer in Cary, NC and I had a diagnosis and it was free and the mechanic looked it over and over and then he took a test drive with me as it was still continuing. At one point we stopped and then we started again and he asked me to push the check mark button on the panel I did and it shows the vehicles current mode it it is in V8 or in V4 mode this he said was the AFM I believe automated fuel management found out that when it goes back to V4 mode it shudders or vibrates until gas it needed to speed up and V8 mode kicks in and it goes away. I found out that I could override it with a device I can use to plug into my OBD port I bought it put it in and not my problem has disappeared. I am now looking to possibly recover the stolen funds I paid fix a problem that was not needed. Do I have a case and where do I go? Help