The full name of GPS is:

Here are the answers to your questions:

5.4:
The full name of GPS is:

• Global Positioning System

5.5:
The parts of speech for the underlined words are:

• to: Preposition
• congestion: Noun

5.1.6:
The punctuated sentence is:

• Exploring alternative modes of transportation can be cost-effective.

5.1.7:
The completed tag question is:

• It is better to use public transportation to reduce costs, isn't it?

5.1.8:
The sentence rewritten into reported speech is:

• He exclaimed that regularly reviewing transportation costs could help stay within the budget.