Jerky manual transmission

2007, Honda Accord sedan. It was used as a lease for about 3 years. Purchased it five months ago. Shifts into gears fine, but while accelerating it****** and drags; shifting from 1st to 2nd causes the car to slow down. Many drivers behind me become upset.
Took it to a Honda dealer, they cleaned some gunk out from "somewhere", but that only made it drivable. It continues to***** when shifting from 1st to 2nd. Shifting from 2nd to 3rd and so on is not that bad. But after the light turns green, I shift into 1st and accelerate. The car barely moves! And to make matters worse, I must shift from 1st to 2nd. That is where it******! And while shifting from 1st to 2nd the car almost stops moving forward!

I've driven Honda Accords, manual transmissions, for almost 17 years, and I have never had such a problem.

Another, dangerous, problem: When coming to a stop, I downshift. As I enter into 2nd and the car is slowing to a stop, it will then***** forward, it accelerates forward! I have to hurry up and remove my foot from the clutch and slam on the brakes! What the heck is wrong with this car?