Trucks are workhorses, but factory suspension often feels stiff or sags under a real load. Upgrading to a high-quality kit makes the ride smoother and handles weight better, though a solid setup usually runs about $2000. You have to account for the parts and the labor if you aren't doing the heavy lifting yourself.
Prices for these kits usually dip in the spring during manufacturer rebate events. We want to separate the price of the gear from how we pay for it. Getting your own financing lined up prevents you from getting stuck with high interest rates offered at the mechanic's counter.
The 18-month window is a firm deadline, not a gift. If you still have a balance on the card when that time is up, you will start owing interest on the remaining amount at the standard rate.