I purchased GMC Yukon 09/2023 and use it more than 85% business yet turbo tax is calculating business use at 28% presumably because purchased in Sept? Any suggestions?

Yes, because you placed the vehicle into service in September, your business use for the year is your business use percentage multiplied by 4/12 months. Even if the vehicle was used 100% for business, the percentage for the first year would be 33.33% (4/12 months).

Note that regular depreciation begins on the date the asset is placed into service. Your expense for the year would be 33.33% of the amount that would be calculated if you used the vehicle all year. Depreciation catches up at the end, so you do receive a full 5 years of depreciation if you keep the vehicle in service that long.