I'm sure this has been asked.. but I couldn't find it real quick... so I'll ask. My 2007 Chevy Silverado classic 4x4 has 106k miles... I need to do some maintenance on it, with the transmisison being my main focus... I've heard of the flushing machines...but highly expensive... whats the difference between that and just dropping the pan? Is there a way I can do the flush myself if that's the preferred method? I'm planning a 1600 mile trip around Christmas, pulling a trailer...want to make sure everything is ready to rock!