Get the engine up to normal running temperature, put the gear selector slowly in and out of all gears, holding it in each gear for a few seconds (this ensures ATF pumped throughout gearbox) .. make sure you are on level ground, and with engine ticking over check Automatic Transmission Fluid . If it needs topping up, use "Dexron" ATF ... easiest way to top up is use a length of plastic tube (about a foot) ... put one end down dipstick tube with a small plastic funnel inserted in other end of plastic tube and pour small ammount each time in to funnel ... Do not overfill !!