Without knowing more...With a 4.2% mortgage, I wouldn't pay it off. Depending on your marginal tax rate, your effective rate is even lower than the 4.2%. Assuming you are working and have good job security, I would let the mortgage roll. Put the money you would put toward extra mortgage payments into an investment account.
The truck is still financed at a low rate (relatively), but I could understand the desire to go ahead and pay it off. That would be the only one of the two I would consider.
