out of gas? buick lasaber

Hope you can help. We have an older buick la sabre, with 230k
well cared for, (wife) and as of late, it does ''this''. When the gas
tank has about 3gals in it, the car will act as if it is out of gas.
We were shopping, and it ran out of gas, and after getting a push to a
station, on a whim I tied to start it, fired right up. It was trouble
free until yesterday (couple of months went by) and the car had about
6 gals in the tank, but it was 'acting empty', sluggish on inclines,
but it would 'settle out' when no hills. After the wife filled the
tank full, it runs find. I went for a spin, it pulled fine, even on a
'good hill' near here.
I "think" it is the fuel pump, (should be the car is old enough) I
bought the car from my brother and I know he did not have to replace
the fuel pump, and we haven't, so that is alot of miles on one pump.I
would just like your ''input'' so when I talk to the mechanic, I don't
sound too stupid. Thanks in advance. cl.

it very well could be the fuel pump, i had the same problem with my buic
lesaber. if not also check the wiring and fuel filters to the fuel pump. i
sold the thing before i got to mess with it. check the hoses as well. my
first bet is the fuel filter though. next off might be the carburator or
the timing chain, if it is either of these you will notice that the engine
runs a lil bumby. like its choking a lilbit and the tempo of the cylinders
will be random. (carburators suck to work on, you would prolly want to
have a mechanic fix it if you dont know lot bout em, to many parts and
they are all small.

the carburator controls the amount of fuel going into the engine, and the
timing chain times everything to its all in sync. on my lesaber you had to
pull out the enging and remove the front of it after draining out the oil
to change it or fix it.

good luck