1991 Buick PA fuel guage

I finally got the cooling problem taken care of on my 91 PA. The low temp coolant fan relay was bad. replaced both the low/high temp relays just to be sure. I have had this problem all along, just thought that the coolant issue was a bigger problem.. The fuel guage will "swing" back and forth. I just keep track of fuel on the mileage trip-ometer, but I would like to fix the problem. I have a 1986 SVO Mustang that I had the same problem with, after I changed the in-tank fuel pump and sending unit, the problem still existed. I fund out that there is a in dash Instrument voltage regulator (IRV) that goes bad, and needed to be replaced. Does the PA have something like this?, or could it just be the tank sending unit...thanks

i have an '89 lesabre. the car had broken brake lines sat for about 6 months with 29000 original miles on it, (grandmothers) so i fixed brake lines and the same day i took it out for its first spin in a long time the fuel pump went bad. now i didnt notice the gauge moving before, but after replacing the pump, tank and sending unit the gauge moves a good amount every time i start stop and accelerate fast. i am assuming it is a problem with my sending unit but since it was such a Bit@@ to get the tank in and out, i am not going to touch it unless i need to. as for a voltage regulator. i have not seen or heard of one on the lesabre. perhaps its something i dont know about.