Thanks!
The business use percentage did vary quite a bit year to year. The 32% was calculated by adding the business mileage for each of the years and dividing that total by the total mileage the truck was driven.
I didn't use the standard mileage rate.
The problem stems from the recent years when I used the truck relatively little for personal use. Consequently, TurboTax allowed a higher depreciation since the calculated business basis for those years was much higher than the total depreciation taken in prior years.
