The 3.3 V6 engines we have are known as "interference" engines, meaning that the valves and pistons will get in each others way if they aren't controlled. And that's the purpose of the timing belt - to keep the timing of the two separate so that doesn't happen.

Sometimes if you're not under any load, the belt can break and the engine just stops. Other times, if there's momentum, the pistons and valves will get in each others way and some serious damage can occur. That's why your mech can't tell you until he tears it down and looks at it which category you fall. If you were at the top of a hill, depending on if you were at the top or just getting there or starting down the other side, you may or may not have been under load. In any case, you could be looking at some damage. But then again, maybe, maybe not. "Do you feel lucky? Well, do you?" (Sorry for the Dirty Harry quote.)

There is one easy way to have prevented this - change the timing belt on schedule (every 105k miles or 7 years). My truck is an '03 and has just 54k miles on it as I only live 3 miles from work. BUT, it's going in probably the end of next week for its first belt change. And I'm at least 2 years overdue. 200k, well, that was just plain asking for it to break.

We all hope yours turns out to on the lesser damage side of things. Plan on it being at least a $1k though as the belt change under good conditions is $800-$1k.

One other thing you should have done. While he's in there, have him replace the other items that require the same tear down to replace - water pump, thermostat, drive belts, etc. That way you save on labor (he'll be putting in new parts instead of the old ones that could then break) and you end up with a more reliable truck.

Fingers crossed for you!

-G