Well, it was definitely the water pump. I just finished putting the new one in and went for a test drive. It was great. No vibration to speak of. Since I had to replace the water pump, I decided to change out the bypass hose as well. I didn't want to put it all back together and have the bypass hose leaking (it is that little hose that connects to the top of the water pump--you know, the one you can't get to). Anyway, it wasn't too difficult to replace once I realized that I could get to it if I removed the accessory mount. The accessory mount comes off after removing a few bolts, you don't have to take off the AC compressor or alternator. In addition, removing the mount enabled me to get to the surface where the water pump seal goes so that I could clean off the remnants of the old seal better. No leaks and no more vibrations, I am one happy man. Thanks for all the help.