Electric jack - unrealistic expectations or bad unit?

Might also check to make sure the grounding wire has a good patch of bare metal and is tight. A poor ground might be causing it to not draw the proper juice. I also have a 18" and use a couple 2x12's at home under it or sometimes a few lynx lever blocks if it's on a site that is sloped forward. Bought mine used for a great price or I would have gotten the longer throw version myself. Great jack so far (2 years).