Man, I never heard of your car beginning to run poorly because a timing belt was needing changed.... I can't imagine how "stretched" it would have to be to effect the performance that much.... maybe I've just never BEEN there? On the OTHER hand, mine failed when the car was running like a "raped ape".... (I always change them well in advance ANYWAY.... at least, ever since I SNAPPED one at the top of fourth headed South on I-75 into Dayton on my '84 Supra at about 97k miles.... I was just about to shift at redline, then.... like the "Back to the Future" Delorean lost motor/power/everthing just before the run for the lightning bolt...)
My experience has been that the only timing belt related SYMPTOM I have had was when a camshaft "jumped time" and I had to reset it... this happened a couple times at around 200k miles on the Supra when the cam bearings began to "gall" just a little and "squeal" at startup, until the teeth would "pop a tooth" or more and then the car ran like SHLIT! (It was OBVIOUS...)
I suspect some OTHER issue, ignition, fuel delivery, timing.... ON TOP of perhaps a timing belt change. My rule of thumb would always be.... if the mileage warrants a timing belt change, and you don't KNOW if it's been changed, CHANGE IT. Don't test your fate on chance on consumables of such magnitute in terms of vehicle operation. (I don't know about these Solaras, but the Toyotas generally have enough clearance NOT to bend valves if the belt breaks.... whereas on a Honda, you are SCREWED if you snap a belt...)
Good luck.
-crisp
