I have a 1998 Chevy Malibu, V6, engine won't turn over.?

Ok, here's the scoop, I own a 98 Chevy Malibu, V6, 3100 engine. The other day I was on my way to work when my car died on my suddenly. I had enough momentum to pull into a parkinglot. I got the car started, it would run, really rough, and then kill after about 10 seconds. We had it towed home, replaced the fuel filter and starter, still no luck. The engine cranks over VERY slow. Did a little reading in our Haynes book, and found the section on the Crankshaft Sensor. While reading it, it described A LOT of what's going on with our car. The check engine light came on a while back, took it in, ran a diagnostic check, came up misfire on cyl #5, even after replacing all plugs & wires. Had it towed to the shop, mechanic REFUSES to look @ the sensor and says the engine is seasing up. Is this and or can this indeed be the case? My gut tells me otherwise... can someone help? Thanks!!