Further manufacture: Use after manufacture treated same as the sale

We purchased a one-year-old truck with a gross vehicle weight rating (GVWR) below 33,000 pounds. We modified the truck so that it now has a GVWR greater than 33,000 pounds. Although we are not sure, we think that the modified truck is probably subject to federal excise tax under IRC Section 4051. However, we intend to sell it tax exempt to the state community college in mid-November. In the meantime, the state community college has agreed to let us use the truck in our business. Because we will ultimately sell the truck in a tax-exempt sale, we do not believe we need to pay any tax on our use of the truck for an approximately two-month period. Is this correct?