Currently have a 3.55 geared rear(3.54 front) diff in my Cherokee. Its a base model so its got 9 inch brakes in the rear. I'm really close to doing a front and rear diff swap with a set of 4.11 diffs. The rear diff I'm putting under my Cherokee has 10x1.75 brakes. The 9 inch rear brakes feel REALLY weak and sketchy when coming down inclines. In a perfect world, will the 10 inch brakes be much of an improvement over the 9 inch brakes?

None you need to uppgrade the booster to newer dual model google it you will double your brakeing power

I wouldn't say *none* but definitely upgrade the booster. If you really want rear brakes skip the drum crap and put discs on

Factory single diaphragm brake set up is scary even with stock tires its a waist of time and money attempting any brake upgrade unless the boosters done also.

What years have the better boosters and is it a straight swap..can i run my old master or do i have to get a different master as well?

Anything newer than 96 has a dual diaphragm master cylinder and booster. Direct replacement.