In the old days you would have to double clutch to get the clutch up to speed or down in speed before shifting into the next gear. ON an automatic at higher speed you need to give it a little gas while dropping it into drive - easy if you have a tach - if not then just rev the engine a little while shifting it - ther still is a clutch that engauges and a little help by getting the engine up to speed helps.
Hey guys my brother almost started screeming when I asked him about coasting with the engine off with an automatic. Seems I was right the for more reasons than I thought. FIRST DON"T DO IT!! Keep the engine running. It turns out the transmission is not splash or oil bath lubricated it is fed oil by the pump run by the input shaft connected to the engine. The first thing that goes at speeds over 20mph within minutes are the SEALS!!! As indicated by a puff a smoke out the filler dipstick pipe. Once the seals go all hell can break loose as hydralic valving will start to fail. So you don't do any mechanical gear damage right away just cook the seals. On some transmissions there are three diagnostic plugs on the side that are the high pressure oil from the internal pump, the regulated pressure from the pump regulator and sometimes the govenor oil pressure feed that determines shift points. If you really want to coast with the engine off, add a pump to feed pressure to the first fitting to lubricate the tranny. Better to just keep the engine running.