Jim Cramer answers questions from Twitter followers about Ford, UPS and Caterpillar. Cramer talks about today's auto sales and which auto stock he likes the most. Cramer is asked whether United Postal Service is considered a buy at these levels and he gives what he thinks is a good entry price. Another follower wanted to know whether Caterpillar's revenue forecast for 2014 was a sign that the world economy would be slowing. Cramer thinks Caterpillar is becoming more domestic than global.