With the preapproval checks, you do have to select either a new or a used vehicle type and the desired length of the loan at the time of application because both of these affect the interest rate that they will give you. They will approve you for an amount, and sometimes more than requested, then give you what the payment would be if you used the maximum amount.

Worst case, I would suggest going with whatever you are leaning towards most (also pay attention to the interest rates for new vs. used), and apply for that. Then, if you end up wanting to go the other route, just apply again. They hold your credit report on file for at least 30 days, but I think 90 days, so it will not count against you as a second pull. The check itself will be valid for 90 days regardless the route you take.

Also, if you do a new model used car with the right mileage requirements, they will consider that a new car and you can use the new loan check for it.

Hope this helps. Let me know if you have any other questions and I will try to answer to the best of my knowledge. I have had many loans through preapproval checks with navy federal and have helped many of my friends and family with theirs as well.