03 tacoma tire bounce problem(HELP)

I BOUGHT AN 03 TACOMA 4X4 AUTOMATIC,I DID ALL THE MAINTENANCE,UPPER BALL JOINTS,LOWER CONTROL ARM BUSHINGS,RACK BUSHINGS,REBUILT DRIVESHAFT.COMPLETE STRUT ASSEMBLYS AND REAR SHOCKS,ALL FLUIDS AND FILTERS. I SPENT A TON OF MONEY.
WHEN YOU HIT EVEN THE SLIGHTEST BUMPS IN ROAD THE WHEELS AND TIRES BOUNCE OUT OF CONTROL ,ESPECIALLY THE FRONT.EVEN AT SLOW SLOW SPEEDS ON GRAVEL THE TIRES BOUNCE OUT OF CONTROL , U HAVE TO COME TO A CRAWL. I HAVE CONTACTED BROWNS TOYOTA AND WE RESEARCHED THE VIN# AND THIS TRUCK CAME WITH THE 16 INCH WHEEL UPGRADE.
WHEN I BOUGHT THE TRUCK IT HAD NEW 265/70/R16 MASTERCRAFT AT TIRES. I TRADED THEM IN ON SOME TOYO STREET TIRES OF THE SAME SIZE. I THOUGHT THIS FIXED THE PROBLEM, BUT SIGH IT DID NOT. ON THE LAST DIRT ROAD TO THE HOUSE I HIT A SMALL HOLE IN THE ROAD, THE TIRES STARTED BOUNCING AND MY HAND SLIGHTLY TURNED THE WHEEL. WELL WHEN THE TIRES STOPPED BOUNCING I CHANGED LANES!!!!I HAVE SEARCHED FOR 15 INCH WHEELS AND IN THE PROCESS TALKED TO SEVERAL PEOPLE THAT HAVE CHANGED FROM 15 INCH TO 16 INCH WHEELS AND TIRES AND DO NOT HAVE THIS PROBLEM.
I TOOK THE TIRES AND WHEELS OFF MY 86 MODEL WHICH ARE 15 INCH AND PUT THEM ON THE 03 TACOMA AND THIS SOLVED THE PROBLEM.SO WTF?
TOYOTA CANT TELL ME IF THE TRUCK SHOULD HAVE STRONGER STRUTS OR NOT.
THEY ALSO CANT TELL ME WHAT TO DO ABOUT THE SPEEDOMETER IF I DO CHANGE TO 15 INCH WHEELS AND TIRES.
SO IF ANYONE HAS ANY INFORMATION ON THIS PROBLEM I WOULD BE GRATEFUL FOR THERE HELP.THANKS