98 Nissan Frontier Suspension

Purchased truck last year and have been satisfied with performance overall. However, within the last two months the the top leaf spring, on both sides of truck have broken. Discovered problem when I went to have rear shocks changed. Mechanic would not let me drive truck off their property. He said that the only thing holding axle on was a small clip that hold springs together. It was apparent that axel had shifted. Had truck towed to spring shop, were they built spring and installed for 160 cdn. I asked the spring mechanic to check other side and he said it appeared OK. Last week went over speed bump, and felt metal on metal. Right spring broken. Another tow, another 160 dollars. For a truck that is only 7 years old, the breaking of two leaf springs appears to me to be premature. The truck is a 2 wheel drive and was not abused by previous owner. anyone have similar problems ?