Beer Body

brewed a Smoked Porter from a recipe generated by BeerSmith2. After 5 weeks n the bottle, the taste was excellent but it seemed to lack body. I wasn't as "thick" as the Porters I've had. I'm calling this BODY for lack of a better definition. Is there a secret to brewing a "thicker" beer or does it have to do with the grains chosen?

Was it an all grain recipe?  Mashing at a higher temp, say 154F will give a beer more body.  Also, try a little dextrin malt like Carapils (I think that is the name) to add some body. 

Actual body and the perception of body can be two different things.

The final gravity of the beer gives you an indication of the real body. Beers finishing from 1.012 to 1.018 will tend to have "medium" body by most people's palate.

The perception of body is influenced by a number of factors. The following list all have the effect of "lightening" the perception of body in beer:

Carbonation (higher levels, lighter perception)
Alcohol (more alcohol lightens body)
Alcohol source (kettle or fermenter sugars add alcohol & lighten body)
Serving temperature (lower temps hide flavor and richness we associate with body)
Foods you've eaten (richer and fattier foods tend to lighten the perception of body)
Balance (perfectly balanced beers can seem bland)
Astringency (has a drying effect)
Residual Sweetness (sweeter beers seem fuller bodied by contrast)

There's a point where each of these become dominant and obvious, thus no longer count towards just body. The main point is to identify if the problem is in perception or process. Perception issues can be changed with simple recipe adjustments. Process issues (like low mash temperature) will change all of your beers, hopefully for the better.