When driving down the RD and at certain RPM when the car shift into gears usually 2 and 3rd gear it JERKS hard almost like it shift hard into gear.. My car been maintenance and had a complete fully flush done, harmonic balancer replace and belt. This has happen few times before not as hard as recent. Nobody can not figure this out, no codes come up and no dash lights come on.

the shaking only occurred sometimes, so a lot of people could not detect the problem. They all thought i was crazy. But the shaking would start after driving it for more then 6 miles and then the truck would start shaking when i reached the speed of 40 and would stop after a second. I'm still trying to get this problem solved.