The 3-speed was standard, while the 4-speed (3+1) was optional. I had the 3-speed for years on one of my jeeps, and I never had an issue with it.
Bad fuel guages are a problem we all deal with. Could be a bad guage. Could be a bad sender. Could be a bad ground, or any number of wiring issues. John Strenk has a whole website with problem-solving for the guages. The only crappy part is that the aftermarket "oem" options are even worse quality then the factory.
That said, if you are going to drop your tank for a repair/replace, thats a good time to swap in a new sender. Dropping the tank is no fun. I've done it about 5 times in the last 4 years (3 to replace the sender, and 2 to fix a leak).