Being a Toyota Truck owner for nearly 40 years, I was wondering about the timing belt failure ratio myself.
Here at home the dealer is pretty big & a couple years ago I asked the service mgr. how many timing belts they had replaced & asked also how many failures that required engine replace or rebuild.
He had work there over 5 years & guessed they had done 100+ timing belt replacement, most with water pump.
He recalled only 3 with engine failure because of timing belt, & 1 of those was a because of idler or pulley failure, he said.
2/3 failures for this area & the volume of business their service dept. does puts up a big ? as to is it really needed @ 90,000 ?
A friend has a 04 DC 4x4 with 363,000 miles with original timing belt. He just had engine failure because of overheating, & bought a used engine to switch, lucky found one with 88,000 miles for $1200.
Another has a 07 DC 4x4 with 220,000 miles with original belt
I have 05 DC 4x4 with 165,000 miles, (But I do have timing belt/water pump on hand to replace)
Although the timing belt failure is costly, I am not sure that the requirement at 90,000 miles to replace is justified except for personal satisfaction that the preventative maintenance will insure owner's worrys about future failure.
David