I would say it's a fairly big deal. Your truck is much newer than mine but I think some of the systems affected would be the same. On a 95, when the crankshaft sensor (called engine speed sensor on the 95's) fails, the engine will run but you have no OD, no lockup, no AC, no cruise, and no alternator charge.
It could be just connectors or ground that need to be cleaned. Sometimes a bad belt (frayed) can damage the wires to the sensor. It's easy to replace and will run between $100 (NAPA) or $150 at dealer.