Got new truck 6000+lbs in July 2018 and want to deduct the full cost ($55k) - used 100% business - but TurboTax only gives me deduction of $7,500. Why not a full $55k?

Check your entries.  In the first place, you need to make sure you select that the vehicle is a 6000-lb+ vehicle when you describe it.  It will ask you for all of the mileage, etc., and calculate the standard mileage rate.  You must make sure that you click the radial that you wish to compare the actual expenses of the vehicle.  Later, after you enter the vehicle price, you will be asked questions about Section 179.  However DO NOT SELECT SECTION 179.  Instead, choose SPECIAL DEPRECIATION located underneath the Section 179 questions.  It is the Bonus Depreciation, and not Section 179, that will allow you to deduct the full price.  (Section 179 is capped at $25,000 for a 6000-lb.+ vehicle).

I have the same situation and it will not work for me. I never even get the 179 question. Tried it many different variations now.

I have a very similar issue.  If I want to deduct the 90% business portion cost of the truck, do I enter this in the Vehicle List or in the Asset section in turbo tax?  In the vehicle list, I couldn't get it to ask me about sec 179?