Why doesn't turbo tax premier guide me with questions on how to report sale of old car and purchase of new car for personal and 5% business use?

Here's how to report sale of old car and purchase of new car for personal and 5% business use:

Step 1:  Determine if you have a Gain.

1. Using your original cost and the total miles since you bought the vehicle, determine  the business percentage.
2. Apply that business percentage to the purchase price and selling price.  Use ALL depreciation.
3. Is there a gain?  If not, go to Step 2.

Step 2:  Determine if you have a deductible Loss.

1. Using the Fair Market Value when it was converted to business use and the total miles since you started using it for business, determine  the business percentage.
2. Apply that business percentage to the purchase price and selling price.  Use ALL depreciation.
3. Is there a gain?  If not, go to Step 3.

Step 3:  You don't have a Gain or a deductible Loss.  Just tell the program you converted the vehicle to personal use, and that is all you need to do.

Regarding the 5% business use of then new car, you can refer to this TurboTax article for information about how to deduct it.