7.25 Gear Swap

BEING THAT I'M PLANNING TO KEEP MY 7.25 FOR A WHILE BEHIND MY MILD 318 AND 904 W/SHIFT KIT COMBO, I WOULD LIKE TO CHANGE SOMETHING. THE CAR, AS DISCUSSED BEFORE, IS BEING USED FOR CRUISING AND PERIODIC HARD ACCELERATION JAUNTS, BUT NOT DRAG DUTY. IT NEEDS TO LAST ME FOR QUITE A WHILE, SO IM TAKEN GOOD CARE OF IT AND ITS IN GOOD HEALTH. IT HAS 2.76 GEARS. WOULD 3.21 GEARS GIVE IT A LITTLE MORE RESPONSIVENESS AND MAINTAIN GOOD FREEWAY RPM'S? i CURRENTLY TURN ABOUT 2100 AT 65 MPH. I WOULD LIKE TO TURN NO HIGHER THAN 2700 WITH 3.21'S. IF I TOOK IT SOMEWHERE TO GET IT DONE, ABOUT HOW MUCH WOULD THEY CHARGE ME FOR THE PARTS AND INSTALLATION OF THESE GEARS? I KNOW A DIFFEREBT REAR WOULD BE OPTIMUM, BUT NOT RIGHT NOW.THANKS FOR ANY REPLIES.