newbie needs advice for 5100's

I've got a 2006 Double Cab long bed, SR5. It came stock with the 245 tires. I also have an ARE topper on the bed that adds some weight to the rear.

I want to get a more aggressive look for my truck, as it appears a little wimpy with the 245 tires. I don't do a lot of offroading, just some occasional beach driving.

I wanted to put the 5100's on all four corners to get a little lift, and add 265x75r16 tires. I have never gotten the rear leaf TSB done, and I am not dissatisfied with my current ride.

After doing all the research that I could, I believe I have to add some kind of lift to the rear to get the truck level if I want to set the fronts at 1.75". My question is, do I need to get the TSB rear spring fix, or can I add a spacer (or block, I'm not sure of the correct term) to the existing springs? I am still under warranty. Could someone advise me of what my options are/what to do? Any help would be appreciated.

 

Interestingly enough, I said this in his other thread (didn't realize the multi threads):