Like everybody else said, 155° shouldn't really give you thin / watery beer. If you are attenuating down to 1007, you are probably mashing at perhaps very low gravities. 155° mash will create less fermentable sugars and more dextrins, etc. 1007 is super low for such a mash temp but this all depends on OG.
Like everybody else said, you are either mis-calculating the temp or mashing lower gravities than you think you are. Your mash efficiency might be the problem so many increase your grains to account for that if you truly believe your temps are correct...
Other than that, I'm not sure what else it could be. Recipes, pH, OG might give us a better understanding of the problem.