What really has me down about this beer is how thin it is. There's really no reason for a beer that is 30% flaked wheat, 23% wheat malt and 8% oats to be anything less than very dense unless it became infected -- it didn't -- or there was a process problem. So I obviously have a process problem.
Since there is no sour or off yeast flavors to suggest an infection, the process issue has to be pre-boil, which means it's all about me. The most likely culprit is low mash temperature causing a highly fermentable beer. I tested my thermometer in several different temperatures (the fridge, room temperature and mash temperatures) with two other thermometers. Oddly enough, my brewing thermometer tested a few degrees cooler than the other two so I am probably mashing hotter than I thought. That should produce the opposite effect.
What is probably happening is the mash on these gallon batches is getting too cool as the mash goes on because it lacks the mass to retain enough heat and I am mashing in a pot so there is very little insulation to retain heat. So I guess I'm going to look into purchasing a two gallon water cooler to use as a mash tun.