Do you use grape jam or strawberry? Personally, I make my PBJ sandwiches with Peter Pan peanut butter and strawberry jam, and then I toast the bread lightly.
Grape jam doesn't really exist over here. The most popular flavours are probably strawberry, raspberry, apricot and blackcurrant. It's also common for the jam to contain bits of fruit within; I can't remember if you guys do the same, or tend to have it smooth.