The transmission, if like my 1978, is supposed to start out in 2nd gear because the car is geared so low. If you floor it upon takeoff and hit the switch, it downshifts to 1st and will run through all 4 speeds (3 shifts). The rod on the left side of the engine controls the shifting. Pull the swivel joint off of the pin, behind the exhaust manifold, and screw it deeper onto the rod. That will make it shift later, at higher rpm's. If you unscrew it and it will shift sooner. Try one turn at a time and tighten the locknut against the swivel joint. The Benz service dept. will give you the correct shift speeds, or you can dig up that information.