I agree with F5fstop. With the auto you just sit back like you aer in a tank and roll over stuff its amazing.
Maybe 1 or 2 miles less MPG with the auto(Doesn't sound like a lot but with gas over $3.00 a gallon here) that is a lot.
The standard should have a little better pickup but not so much that you would notice or care. The truck is big so you aren't going to be fast any way you look at it.
Summary : really depends on what kind of driving you are going to do but me with the 12% city roads I don't want to even think about a standard. Some parts of downtown Seattle are like SanFrancisco streets.
Even in the auto it may creep back a little at start off.