Them auto boxes our mercs start of in first or second gear sometimes as your pulling off it changes back to first ,I always flick switch to second hit power button then pull of when I get to 12 mph I put it on cruise control to 55 then let the box work it’s way up with out touching the accelerator,if I got 14 tonne on going up banks down to 29 mph and it keeps changing down bring back the old gear box and clutch I say