Didn't your car roll out with 155SR15 or 5.60-15 on it? The size you're looking for is nearly 2 inches larger diameter than those. 195/60, 195/65, and 185/65 are all much closer to correct diameter and give you a lot of choice. Sears distributed tires are often not exactly the same product you would get from a Bridge/Firestone, Dunlop, Goodyear, Michelin, etc dealer.

You can help determine the speedo error by finding a road with mileage posts. Check the odometer against them for a few miles. If it's a similar error to the speedo, then the drive gear doesn't match your final drive. If the odometer is close, then you'll find that driving 60 seconds at 60 mph doesn't record 1.0 mile, meaning speedo calibration.