Thanks to everyone who took the time to reply to my question. It is greatly appreciated. Thanks too to Tim11 for the review link. I did check it out along with the Sigma and Nikon lens. One thing I noticed is the Tamron and Nikon share some of the same weaknesses.

Please keep in mind I am not a professional making a living taking photographs. Nor am I the expert like most of you. I understand some of the remarks made in the reviews but many go over my head. I have heard about quality and color issues at the extreme zoom settings. But from what I understand and from the way I use my camera it is very unlikely that these shortcomings will affect the kind of pictures I will be taking.

Today I stopped by Tuttle Camera in Long Beach, CA just to see for myself which way to go. Two of the sales people said I would be much happier overall with the Tamron. Yes they did mention color & quality issues at the extreme zoom settings. One sales rep even commented the auto focus was faster with the Tamron vs Nikon.
I then asked about Sigma and they said not to even consider. One rep said he had 2 Sigma lenses break on him. He is much happier with Tamron.

Thanks again for taking the time to help this novice. Now I just need to work on raising the $$ for the purchase. Take care.