I started laying my first room of solid prefinished 3/4 5" planks. Things progressed awfully slow as I got used to the tools etc. However my progress was going backwards as I had to lift some planks because I was not satisfied with the gaps, I chalked it up as being inexperienced. I finally cheated in the closet and made sure 1 row was again perfectly straight and only on the next row did I notice that my 5" was probably + or - 1/16 to 1/8". I don't know if I can generalize yet but I think the smaller length boards have greater differences.

So, is this normal? I finally now know that I have to watch the transitions from board to board and shim as I go to at least split the gaps if the next line is also over/under 5". BUT, as I laid a few more rows I was really wondering what a Pro would do.

By the way, I'm suppose to have Clear grade.

It's sounds to me like the milling of the prefinished product is bad. One way to check is to measure the width of the boards. There should be much less a difference than what you have suspected. If the milling is really as bad as you say, you should have some really nice sized gaps in your new floor. Another way to know how good the milling is by going by price. 95% of the time you get what you pay for. $1-$2 sqft (the noname internet special) you're better off sanding and refinishing the subfloor. $2-$3.5 sqft (menards timberfalls collection) you'll have some unlevelness issues and usually big bevels to hide it. Anything above $5 sqft youll get a good floor and the bevels will get smaller as you spend more money. This is just a good rule of thumb but not always true. I installed a mohawk floor for a customer once and it had the 1/8" narrow boards all over. If you are ok with gaps, keep plugging away but if the product bothers you, now is the time to talk to the company and get some money back.
Hope this helped

Thanks, your post did help.

I have alerted my supplier and will have 2 options if he agrees that milling is bad: 1) additional flooring to offset square footage agreed to or 2) Return & Refund. Looks like I am going to investigate option 1.

glad to hear it. Hope it all works out