Can a very high mileage ( 150,000 miles) timing belt stretch enough to slip one tooth so the the engine still runs but not full power? A friend said her car was not running well so took it to mechanic who took off a cover and said her timing belt was bad and had slipped. Soon after the belt broke.
I had a problem like this on my car, turns out there was a recall for my specific model of Honda Accord because there was a design flaw in the timing chain and/or tensioner
If I had registered the VIN with Honda when I bought it, the nearest Honda dealership would have fixed it for free but I didn't until years later so had to shell out for it myself. I did this before the belt broke however
Hope that helps