Hybrid Truck Incentives Improvement Act - Amends the Internal Revenue Code to: (1) extend through 2015 the tax credit for the purchase of a new qualified hybrid motor vehicle, (2) increase the incremental cost levels for computing credit amounts for such vehicles, (3) allow a 10% credit for comparable vehicles that achieve an increased city fuel economy, and (4) allow a credit for electric vehicles with a gross vehicle weight rating of not less than 8,500 pounds.