I'd also say your pieces are a little large for Asian deep fry. This might also be another time to watch out for overloading the pan and getting too much temperature drop in the oil. If you're using a thermometer watch how much the temperature drops as you add the food to be fried.
If you're trying to fry at 350, maybe heat it to 380 before starting to fry to account for the temperature drop, and stop adding food when the oil hits 350.
Also, you need to construct more of a batter than a marination and dry dredge will build.
From http://chinesefood.about.com/od/pork/r/sweetsourpork.htm here is their batter ingredients as an example.
1/3 cup flour
1/3 cup cornstarch
1 egg white, lightly beaten
1 tablespoon vegetable oil
1/3 cup warm water, as needed
Battered deep frying is really a steam cooking technique. The batter seals up and the resultant steam helps cook the food inside the batter. Of course some of the steam escapes the batter, helping keep the oil out to a good degree.
For a good deep fry, you have to balance the batter thickness, the size of the item encased in the batter and the oil temperature so that the batter is properly cooked and the interior is properly cooked to completion at the same time.
With such a thin batter coating as you described without much included moisture, you don't get the protective shell and the proper steaming effect. Dry meat results. If you're looking for a velveted type result, you're on the right path, but use a low temperature oil, just 250 F and a very quick cooking time.