I was driving my rig around town today, when the check engine light comes on. Engine seems to be running fine, but the tranny is shifting very firm now, and holding the rpm's before it shifts. Sometimes it takes a while before it goes into 4th and 5th. The truck just turned 1500 miles. I haven't even towed anything yet, but was planning to pull my boat to the coast this weekend. Should I not pull the boat this weekend? What could this be?