Hello and welcome.
This sounds like a very common problem with the fuel level sender. The fuel level sender is a variable resistor that is in the fuel tank, and snaps onto the fuel pump module assembly. There are small "fingers" on the sender that corrode away over time, and cause fluctuations in the gauge. To replace this part, the fuel tank will have to be removed, and the fuel pump module assembly removed. Then you can replace the sender.
With the amount of miles and year of the truck, i would highly suggest that if going to have this done, to go ahead and replace the fuel pump assembly while it is removed. Fuel pump failure is a common thing on these trucks with alot of miles, that can cause engine to stall and not restart. If going this far to replace level sender, it would be a good idea to replace fuel pump assembly since it will already be reromved, but that is up to you.