Take the shell off and see where there's room to add weight. BB's are a possibility, your LHS has lead weights that look kinda like a flat metal tootsie roll, you can break off one at a time and add them where they'll fit - they even come with sticky foam tape attached for mounting. I think each square is 1/4 oz(??) How steep is your grade?? Keep in mind even a "mild" 2% grade is pretty steep on a prototype train line, and would considerably affect the amount an engine could pull. I seem to remember reading somewhere that a 4% grade cut the engines pulling ability by 40% or something. One other alternative - do what the real raidroads did and add another powered unit - an A unit back to back with yours, or a trailing B unit...or do both!! Even on my flatland layout I like to run two engines together, once their "speedmatched" to run together (in DCC) they allow you to run trains smoothly and slowly, and aren't affected by grades the way a single engine is.