It seems to me the simple answer would be a flat platform about 10 inches high that you would back the truck up to
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Whenever possible I keep the backplate attached and walk around them on/off the boat that way. Then I sit on my tailgate and lay them back in the bed of my truck. However I am 6' 1" so you may not be able to reach the bottom of your tanks onto your truck.
Go to the gym, and work on strengthening your back/arms/legs etc. Have someone help you for the time being (I assume you're diving with a buddy?), but you really do need to get in the position of being able to lift them by yourself!