Need to remove the Fuel Tank, not an easy job, unless you have tools and a hoist. But first and foremost, best to get a diagnosis on the problem, just had an Escalade in the shop, this week, where another shop had replaced the Fuel Pump and the Caddy did the exact same that your Caddy is doing. We fixed the problem which was a defective Crankshaft Sensor, which had a code stored on the Computer but did NOT turn on the Check Engine Light. Being forewarned is being prepared. Don't ASSUME it is Fuel PUMP, in my experience in independent shops and as a Journeyman GM Dealership Diagnostic Technician, when a GM Fuel PUMP dies, it just dies. Best of Luck.