Same source? A fish that dies when introduced to a healthy tank is likely either a) sick upon purchase or b) bullied. You will be able to observe the bullying--sometimes you'll need to sit away from the tank a bit to avoid feeding behavior, but it won't be an occassional thing if it's this lethal.
However--I'd suspect that the gouramie is not to blame. Gouramies can be aggressive and territorial, but typically just with each other--they mostly ignore other fish. Algae eaters canbe tough to get in good shape, since the shipping process usually leaves them without food for an extended period of time--this can be lethal in the long run. You might want to verify that you are providing enough food as well--most tanks don't produce enough algae to support one algae eater, so supplementing with wafers and fresh veggies is a must. I'd find a store that will allow you to put a down payment on the fish, leave it in their tank for a week or so, make sure it's healthy before bringing it home.