swapped 13s for 15s steering gear unhappy now

Greeetings,
I recently found some killer rally sbp 15 inch wheels, and tires. they mounted with good clearance on my 64 dart, but right away the steering box feels metallic, and tired, with noise at the end of each turn. Am I dealing with a tired gear box, or has the increase in tire demand just shown it's age. It wasn't so bad with 13 inch tires, but now feels like s--t. Am I just looking at a tired gear, or is there some problems with the 15s? I cant go back to 13s
Thanks so much