You my want to try a different diet but any changes you make should be gradual.
A BML or HPW diet is fed along with fruits and vegetables and mealworms. You can also replace the mealworms with chicken or turkey on occasion. All meat should be cooked plain and unseasoned. You can also cut up meats once cooked and freeze it the same as you do fruits.
I also give them plain or fruit yogurt every other night. This can be fed either as a licky treat (from your finger) or put in their bowl with their other food. Make sure the yogurt does not contain artificial sweeteners which are found in some diet yogurts.
Vegetables
Peas, green beans, carrots, corn (when fed along with other vegetables) ,squash, asparagus, okra, and spinach (in moderation-too much can block calcium absorption) and sweet potato. 
You can buy bags of mixed frozen vegetables at the grocery store.
Fruits
Fresh or frozen papaya, apples, pears, raspberries, blueberries, blackberries, seedless grapes, plums, mango's, watermelon, strawberries, cranberries, apricots, cantaloupe, honeydew melons, kiwi, peaches, bananas etc. Take out pits and large seeds. (Don't worry about the smaller seeds i.e. strawberries, kiwi, etc.) They also love avocado, but feed it in moderation as it is fatty.
Make sure all fruit has been washed really well. You can chop up fresh fruit and freeze it, so they get a good variety and the fruit doesn't go bad before you have a chance to use it up.
Freezing Fruit
Wash, peel and section fruit (leave berries whole), place in a single layer on a baking sheet and freeze 4 to 6 hours or until frozen. Pack in freezer weight resealable plastic bags and store in freezer until ready to use.
Treats
Some treats you can give your Sugar Glider are Yogurt, Apple Sauce, Baby Foods such as (Fruit, Veggie, Chicken, Turkey). Yogurt Drops/Yoggies (can be found at the pet store or in the small animal pet section of many variety stores),along with mealworms, waxworms and crickets (dried and live). There are also vast varieties of Dried Natural Fruits, Chew Stick etc. that are sold on several Sugar Glider sites.