A new member with a ?

I have a 1999 Tacoma prerunner that I have put a 3 inch lift on about three years ago. I had 31-10.50-15s on it and it pulled good with my boat but I decided to put 32-11.50-15s on it. It pulls fine with its own weight but when I go to pull my boat it losses alot of power. My question is what rear end gears would I need to acomadate the bigger tires? I think it has the factory 373s in it now.

 

Thanks. Another question would be. What would be the best decision to make money wise To replace rear end or just put gears in my existing rear end?