2002 Suburban-replacing fuel level sensor

My 2002 Suburban has had delays recently starting up when the engine is cold. It acts like it's trying to start when you turn the key, but would take 5-10 seconds to actually start. Sometimes it wouldn't start on the first time, but then when you turn the key again it would start right up.

Then one morning it wouldn't start at all. Towed it to the dealer, and they said we were out of gas. They added 5 gallons & it started. They said the resistance on our fuel level sensor is out of range, and needs to be replaced. (Gauge shows 1/2 tank when it's empty.)

My question is, they said they have to pull the gas tank out to replace the sensor, but someone told me that after 1997 manufacturers put an access panel on the tanks that make it so you don't have to pull the tank out to replace the sensor. Which is it? Does $550 sound right for replacing the fuel sensor? Is this something a non-dealership mechanic can easily do (estimate of $350)?

Thanks,
John