Just had my sending unit replaced on top of gas tank for 1998 Bonneville SSei. Kept the original gas pump. I park car on hill with a 30 degree incline. Had at least 1/4 tank of fuel but car wouldn't start and heard 3 second buzzing sound when key in run position. Had to put in 5 gallons of gas before car would start. Sound would not be audible with more fuel. Fuel gauge would always show low and low fuel warning light would come on when parked on incline then would show normal fuel level once car driven on flatter surface if I had 1/2 tank or less. I am getting another sending unit and am wondering if fuel pump not resting lower in tank as with original unit?

I hope an Airtex brand pump wasn't installed. They are junk.

Only thing I can think of is, the float isn't floating correctly or the fuel level sensor isn't correct. And of course, the only way to verify this is to drop the tank again.

you should be repalcing the whole assembly with a new delphi unit and new o-ring, there is no access so you dont want to be dropping the tank a hundred times. also the connector is flacky and gets corroded on those back probe with a meter to see if you are getting good power through it, ended up soldering the wires together on my father inlaws 96