This is a big pain as I have done it 4 times. I have had 5 Astros. The 3 steel fuel lines connect to 3 flexible hoses. It goes like this. You have to jack up the rear of the vehicle on both sides and set it on jack stands to give you enough room to work. You then have to remove the plastic shroud around the gas tank. Unplug the fuel pump power and sending unit plug on the frame toward the front. Then you take a board at least one foot by 2 foot and put it on the jack and support the fuel tank. You remove the fuel neck hose connection. You can leave it connected where you put gas in. You have to bend and flex it out of the way and out of the tank. You only let the tank down about 4 inches and then dis-connect the 3 hoses. After the tank is free, I let the tank down onto concrete blocks, move the jack, and then let it down onto 4x4 blocks of wood and then slide them out and pull the tank out from under the van. The unit is held in place by a locking ring. Just take a flatblade screwdriver and a hammer and tap it counterclockwise. You have to lift the unit slowly and turn and twist it to remove the fuel sending unit float. You will see this.
Are you absolutely sure the fuel pump is the problem and dead before you undertake this task?
You can find new fuel pump/sending unit assemblies on Ebay for any big Chevy ie Tahoe, Blazer, Express, Yukon for under $100.
The fuel pump assy has plastic barbed fittings. If a junkyard drops the fuel tank all at once, they break off the plastic necks and ruin the pump. I went for a junkyard pump once, but 13 junkyards ruined the pump, before I learned to ask if it was still in the vehicle. I had to tell them, DONT remove it until I get there.
The quick clip plastic hoses are expensive. They are only about 15 inches long each. If you damage a plastic hose, there is a thing called " air brake fittings". They are brass compression fittings only they have a center tube built in that will both go into the inside of the fitting and compression bite the outside of the fitting.
On my last replacement of an Astro fuel pump, the plastic hoses could not be removed without damage, so I put it back together with high pressure fuel hose and air brake fittings and both the plastic fittings on the pump and the steel lines on the frame. I had to drill out the plastic fittings on the pump maybe 1/32 of an inch, but that has been 30,000 miles ago and it works. (GM wants $120 for the 3 hose set!)
I can do this blindfolded. If you have any questions, email me anytime. Techman1@att. Net